diff --git a/layout/style/ServoStyleSet.cpp b/layout/style/ServoStyleSet.cpp
new file mode 100644
index 000000000000..33bb8d1820cd
--- /dev/null
+++ b/layout/style/ServoStyleSet.cpp
@@ -0,0 +1,191 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ServoStyleSet.h"
+
+#include "nsCSSAnonBoxes.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+void
+ServoStyleSet::Init(nsPresContext* aPresContext)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+void
+ServoStyleSet::BeginShutdown()
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+void
+ServoStyleSet::Shutdown()
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+bool
+ServoStyleSet::GetAuthorStyleDisabled() const
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::SetAuthorStyleDisabled(bool aStyleDisabled)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+void
+ServoStyleSet::BeginUpdate()
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::EndUpdate()
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+// resolve a style context
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ResolveStyleFor(Element* aElement,
+                               nsStyleContext* aParentContext)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ResolveStyleFor(Element* aElement,
+                               nsStyleContext* aParentContext,
+                               TreeMatchContext& aTreeMatchContext)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ResolveStyleForNonElement(nsStyleContext* aParentContext)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ResolvePseudoElementStyle(Element* aParentElement,
+                                         CSSPseudoElementType aType,
+                                         nsStyleContext* aParentContext,
+                                         Element* aPseudoElement)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+// aFlags is an nsStyleSet flags bitfield
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ResolveAnonymousBoxStyle(nsIAtom* aPseudoTag,
+                                        nsStyleContext* aParentContext,
+                                        uint32_t aFlags)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+// manage the set of style sheets in the style set
+nsresult
+ServoStyleSet::AppendStyleSheet(SheetType aType,
+                                CSSStyleSheet* aSheet)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::PrependStyleSheet(SheetType aType,
+                                 CSSStyleSheet* aSheet)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::RemoveStyleSheet(SheetType aType,
+                                CSSStyleSheet* aSheet)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::ReplaceSheets(SheetType aType,
+                             const nsTArray<RefPtr<CSSStyleSheet>>& aNewSheets)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::InsertStyleSheetBefore(SheetType aType,
+                                      CSSStyleSheet* aNewSheet,
+                                      CSSStyleSheet* aReferenceSheet)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+int32_t
+ServoStyleSet::SheetCount(SheetType aType) const
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+CSSStyleSheet*
+ServoStyleSet::StyleSheetAt(SheetType aType,
+                            int32_t aIndex) const
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::RemoveDocStyleSheet(CSSStyleSheet* aSheet)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsresult
+ServoStyleSet::AddDocStyleSheet(CSSStyleSheet* aSheet,
+                                nsIDocument* aDocument)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ProbePseudoElementStyle(Element* aParentElement,
+                                       CSSPseudoElementType aType,
+                                       nsStyleContext* aParentContext)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+already_AddRefed<nsStyleContext>
+ServoStyleSet::ProbePseudoElementStyle(Element* aParentElement,
+                                       CSSPseudoElementType aType,
+                                       nsStyleContext* aParentContext,
+                                       TreeMatchContext& aTreeMatchContext,
+                                       Element* aPseudoElement)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsRestyleHint
+ServoStyleSet::HasStateDependentStyle(dom::Element* aElement,
+                                      EventStates aStateMask)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
+
+nsRestyleHint
+ServoStyleSet::HasStateDependentStyle(dom::Element* aElement,
+                                      CSSPseudoElementType aPseudoType,
+                                     dom::Element* aPseudoElement,
+                                     EventStates aStateMask)
+{
+  MOZ_CRASH("stylo: not implemented");
+}
diff --git a/layout/style/ServoStyleSet.h b/layout/style/ServoStyleSet.h
new file mode 100644
index 000000000000..53150f32bd32
--- /dev/null
+++ b/layout/style/ServoStyleSet.h
@@ -0,0 +1,111 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_ServoStyleSet_h
+#define mozilla_ServoStyleSet_h
+
+#include "mozilla/EventStates.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/SheetType.h"
+#include "nsChangeHint.h"
+#include "nsCSSPseudoElements.h"
+#include "nsIAtom.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace dom {
+class Element;
+} // namespace dom
+class CSSStyleSheet;
+} // namespace mozilla
+class nsStyleContext;
+class nsPresContext;
+struct TreeMatchContext;
+
+namespace mozilla {
+
+/**
+ * The set of style sheets that apply to a document, backed by a Servo
+ * Stylist.  A ServoStyleSet contains ServoStyleSheets.
+ */
+class ServoStyleSet
+{
+public:
+  void Init(nsPresContext* aPresContext);
+  void BeginShutdown();
+  void Shutdown();
+
+  bool GetAuthorStyleDisabled() const;
+  nsresult SetAuthorStyleDisabled(bool aStyleDisabled);
+
+  void BeginUpdate();
+  nsresult EndUpdate();
+
+  // resolve a style context
+  already_AddRefed<nsStyleContext>
+  ResolveStyleFor(dom::Element* aElement,
+                  nsStyleContext* aParentContext);
+
+  already_AddRefed<nsStyleContext>
+  ResolveStyleFor(dom::Element* aElement,
+                  nsStyleContext* aParentContext,
+                  TreeMatchContext& aTreeMatchContext);
+
+  already_AddRefed<nsStyleContext>
+  ResolveStyleForNonElement(nsStyleContext* aParentContext);
+
+  already_AddRefed<nsStyleContext>
+  ResolvePseudoElementStyle(dom::Element* aParentElement,
+                            mozilla::CSSPseudoElementType aType,
+                            nsStyleContext* aParentContext,
+                            dom::Element* aPseudoElement);
+
+  // aFlags is an nsStyleSet flags bitfield
+  already_AddRefed<nsStyleContext>
+  ResolveAnonymousBoxStyle(nsIAtom* aPseudoTag, nsStyleContext* aParentContext,
+                           uint32_t aFlags = 0);
+
+  // manage the set of style sheets in the style set
+  nsresult AppendStyleSheet(SheetType aType, CSSStyleSheet* aSheet);
+  nsresult PrependStyleSheet(SheetType aType, CSSStyleSheet* aSheet);
+  nsresult RemoveStyleSheet(SheetType aType, CSSStyleSheet* aSheet);
+  nsresult ReplaceSheets(SheetType aType,
+                         const nsTArray<RefPtr<CSSStyleSheet>>& aNewSheets);
+  nsresult InsertStyleSheetBefore(SheetType aType,
+                                  CSSStyleSheet* aNewSheet,
+                                  CSSStyleSheet* aReferenceSheet);
+
+  int32_t SheetCount(SheetType aType) const;
+  CSSStyleSheet* StyleSheetAt(SheetType aType, int32_t aIndex) const;
+
+  nsresult RemoveDocStyleSheet(CSSStyleSheet* aSheet);
+  nsresult AddDocStyleSheet(CSSStyleSheet* aSheet, nsIDocument* aDocument);
+
+  // check whether there is ::before/::after style for an element
+  already_AddRefed<nsStyleContext>
+  ProbePseudoElementStyle(dom::Element* aParentElement,
+                          mozilla::CSSPseudoElementType aType,
+                          nsStyleContext* aParentContext);
+
+  already_AddRefed<nsStyleContext>
+  ProbePseudoElementStyle(dom::Element* aParentElement,
+                          mozilla::CSSPseudoElementType aType,
+                          nsStyleContext* aParentContext,
+                          TreeMatchContext& aTreeMatchContext,
+                          dom::Element* aPseudoElement = nullptr);
+
+  // Test if style is dependent on content state
+  nsRestyleHint HasStateDependentStyle(dom::Element* aElement,
+                                       EventStates aStateMask);
+  nsRestyleHint HasStateDependentStyle(dom::Element* aElement,
+                                       mozilla::CSSPseudoElementType aPseudoType,
+                                       dom::Element* aPseudoElement,
+                                       EventStates aStateMask);
+};
+
+} // namespace mozilla
+
+#endif // mozilla_ServoStyleSet_h
diff --git a/layout/style/StyleSetHandle.h b/layout/style/StyleSetHandle.h
new file mode 100644
index 000000000000..b2162e7f88dd
--- /dev/null
+++ b/layout/style/StyleSetHandle.h
@@ -0,0 +1,211 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StyleSetHandle_h
+#define mozilla_StyleSetHandle_h
+
+#include "mozilla/EventStates.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/SheetType.h"
+#include "mozilla/StyleBackendType.h"
+#include "nsChangeHint.h"
+#include "nsCSSPseudoElements.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+class CSSStyleSheet;
+class ServoStyleSet;
+namespace dom {
+class Element;
+} // namespace dom
+} // namespace mozilla
+class nsIAtom;
+class nsIDocument;
+class nsStyleContext;
+class nsStyleSet;
+class nsPresContext;
+struct TreeMatchContext;
+
+namespace mozilla {
+
+#define SERVO_BIT 0x1
+
+/**
+ * Smart pointer class that can hold a pointer to either an nsStyleSet
+ * or a ServoStyleSet.
+ */
+class StyleSetHandle
+{
+public:
+  // We define this Ptr class with a StyleSet API that forwards on to the
+  // wrapped pointer, rather than putting these methods on StyleSetHandle
+  // itself, so that we can have StyleSetHandle behave like a smart pointer and
+  // be dereferenced with operator->.
+  class Ptr
+  {
+  public:
+    friend class ::mozilla::StyleSetHandle;
+
+    bool IsGecko() const { return !IsServo(); }
+    bool IsServo() const
+    {
+      MOZ_ASSERT(mValue, "StyleSetHandle null pointer dereference");
+#ifdef MOZ_STYLO
+      return mValue & SERVO_BIT;
+#else
+      return false;
+#endif
+    }
+
+    StyleBackendType BackendType() const
+    {
+      return IsGecko() ? StyleBackendType::Gecko :
+                         StyleBackendType::Servo;
+    }
+
+    nsStyleSet* AsGecko()
+    {
+      MOZ_ASSERT(IsGecko());
+      return reinterpret_cast<nsStyleSet*>(mValue);
+    }
+
+    ServoStyleSet* AsServo()
+    {
+      MOZ_ASSERT(IsServo());
+      return reinterpret_cast<ServoStyleSet*>(mValue);
+    }
+
+    nsStyleSet* GetAsGecko() { return IsGecko() ? AsGecko() : nullptr; }
+    ServoStyleSet* GetAsServo() { return IsServo() ? AsServo() : nullptr; }
+
+    const nsStyleSet* AsGecko() const
+    {
+      return const_cast<Ptr*>(this)->AsGecko();
+    }
+
+    const ServoStyleSet* AsServo() const
+    {
+      MOZ_ASSERT(IsServo());
+      return const_cast<Ptr*>(this)->AsServo();
+    }
+
+    const nsStyleSet* GetAsGecko() const { return IsGecko() ? AsGecko() : nullptr; }
+    const ServoStyleSet* GetAsServo() const { return IsServo() ? AsServo() : nullptr; }
+
+    // These inline methods are defined in StyleSetHandleInlines.h.
+    inline void Delete();
+
+    // Style set interface.  These inline methods are defined in
+    // StyleSetHandleInlines.h and just forward to the underlying
+    // nsStyleSet or ServoStyleSet.  See corresponding comments in
+    // nsStyleSet.h for descriptions of these methods.
+
+    inline void Init(nsPresContext* aPresContext);
+    inline void BeginShutdown();
+    inline void Shutdown();
+    inline bool GetAuthorStyleDisabled() const;
+    inline nsresult SetAuthorStyleDisabled(bool aStyleDisabled);
+    inline void BeginUpdate();
+    inline nsresult EndUpdate();
+    inline already_AddRefed<nsStyleContext>
+    ResolveStyleFor(dom::Element* aElement,
+                    nsStyleContext* aParentContext);
+    inline already_AddRefed<nsStyleContext>
+    ResolveStyleFor(dom::Element* aElement,
+                    nsStyleContext* aParentContext,
+                    TreeMatchContext& aTreeMatchContext);
+    inline already_AddRefed<nsStyleContext>
+    ResolveStyleForNonElement(nsStyleContext* aParentContext);
+    inline already_AddRefed<nsStyleContext>
+    ResolvePseudoElementStyle(dom::Element* aParentElement,
+                              mozilla::CSSPseudoElementType aType,
+                              nsStyleContext* aParentContext,
+                              dom::Element* aPseudoElement);
+    inline already_AddRefed<nsStyleContext>
+    ResolveAnonymousBoxStyle(nsIAtom* aPseudoTag, nsStyleContext* aParentContext,
+                             uint32_t aFlags = 0);
+    inline nsresult AppendStyleSheet(SheetType aType, CSSStyleSheet* aSheet);
+    inline nsresult PrependStyleSheet(SheetType aType, CSSStyleSheet* aSheet);
+    inline nsresult RemoveStyleSheet(SheetType aType, CSSStyleSheet* aSheet);
+    inline nsresult ReplaceSheets(SheetType aType,
+                           const nsTArray<RefPtr<CSSStyleSheet>>& aNewSheets);
+    inline nsresult InsertStyleSheetBefore(SheetType aType,
+                                    CSSStyleSheet* aNewSheet,
+                                    CSSStyleSheet* aReferenceSheet);
+    inline int32_t SheetCount(SheetType aType) const;
+    inline CSSStyleSheet* StyleSheetAt(SheetType aType, int32_t aIndex) const;
+    inline nsresult RemoveDocStyleSheet(CSSStyleSheet* aSheet);
+    inline nsresult AddDocStyleSheet(CSSStyleSheet* aSheet, nsIDocument* aDocument);
+    inline already_AddRefed<nsStyleContext>
+    ProbePseudoElementStyle(dom::Element* aParentElement,
+                            mozilla::CSSPseudoElementType aType,
+                            nsStyleContext* aParentContext);
+    inline already_AddRefed<nsStyleContext>
+    ProbePseudoElementStyle(dom::Element* aParentElement,
+                            mozilla::CSSPseudoElementType aType,
+                            nsStyleContext* aParentContext,
+                            TreeMatchContext& aTreeMatchContext,
+                            dom::Element* aPseudoElement = nullptr);
+    inline nsRestyleHint HasStateDependentStyle(dom::Element* aElement,
+                                                EventStates aStateMask);
+    inline nsRestyleHint HasStateDependentStyle(
+        dom::Element* aElement,
+        mozilla::CSSPseudoElementType aPseudoType,
+        dom::Element* aPseudoElement,
+        EventStates aStateMask);
+
+  private:
+    // Stores a pointer to an nsStyleSet or a ServoStyleSet.  The least
+    // significant bit is 0 for the former, 1 for the latter.  This is
+    // valid as the least significant bit will never be used for a pointer
+    // value on platforms we care about.
+    uintptr_t mValue;
+  };
+
+  StyleSetHandle() { mPtr.mValue = 0; }
+  StyleSetHandle(const StyleSetHandle& aOth) { mPtr.mValue = aOth.mPtr.mValue; }
+  MOZ_IMPLICIT StyleSetHandle(nsStyleSet* aSet) { *this = aSet; }
+  MOZ_IMPLICIT StyleSetHandle(ServoStyleSet* aSet) { *this = aSet; }
+
+  StyleSetHandle& operator=(nsStyleSet* aStyleSet)
+  {
+    MOZ_ASSERT(!(reinterpret_cast<uintptr_t>(aStyleSet) & SERVO_BIT),
+               "least significant bit shouldn't be set; we use it for state");
+    mPtr.mValue = reinterpret_cast<uintptr_t>(aStyleSet);
+    return *this;
+  }
+
+  StyleSetHandle& operator=(ServoStyleSet* aStyleSet)
+  {
+#ifdef MOZ_STYLO
+    MOZ_ASSERT(!(reinterpret_cast<uintptr_t>(aStyleSet) & SERVO_BIT),
+               "least significant bit shouldn't be set; we use it for state");
+    mPtr.mValue =
+      aStyleSet ? (reinterpret_cast<uintptr_t>(aStyleSet) | SERVO_BIT) : 0;
+    return *this;
+#else
+    MOZ_CRASH("should not have a ServoStyleSet object when MOZ_STYLO is "
+              "disabled");
+#endif
+  }
+
+  // Make StyleSetHandle usable in boolean contexts.
+  explicit operator bool() const { return !!mPtr.mValue; }
+  bool operator!() const { return !mPtr.mValue; }
+
+  // Make StyleSetHandle behave like a smart pointer.
+  Ptr* operator->() { return &mPtr; }
+  const Ptr* operator->() const { return &mPtr; }
+
+private:
+  Ptr mPtr;
+};
+
+#undef SERVO_BIT
+
+} // namespace mozilla
+
+#endif // mozilla_StyleSetHandle_h
diff --git a/layout/style/StyleSetHandleInlines.h b/layout/style/StyleSetHandleInlines.h
new file mode 100644
index 000000000000..0ac60234295d
--- /dev/null
+++ b/layout/style/StyleSetHandleInlines.h
@@ -0,0 +1,213 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StyleSetHandleInlines_h
+#define mozilla_StyleSetHandleInlines_h
+
+#include "mozilla/ServoStyleSet.h"
+#include "nsStyleSet.h"
+
+#define FORWARD(method_, args_) \
+  return IsGecko() ? AsGecko()->method_ args_ : AsServo()->method_ args_;
+
+namespace mozilla {
+
+void
+StyleSetHandle::Ptr::Delete()
+{
+  if (mValue) {
+    if (IsGecko()) {
+      delete AsGecko();
+    } else {
+      delete AsServo();
+    }
+  }
+}
+
+void
+StyleSetHandle::Ptr::Init(nsPresContext* aPresContext)
+{
+  FORWARD(Init, (aPresContext));
+}
+
+void
+StyleSetHandle::Ptr::BeginShutdown()
+{
+  FORWARD(BeginShutdown, ());
+}
+
+void
+StyleSetHandle::Ptr::Shutdown()
+{
+  FORWARD(Shutdown, ());
+}
+
+bool
+StyleSetHandle::Ptr::GetAuthorStyleDisabled() const
+{
+  FORWARD(GetAuthorStyleDisabled, ());
+}
+
+nsresult
+StyleSetHandle::Ptr::SetAuthorStyleDisabled(bool aStyleDisabled)
+{
+  FORWARD(SetAuthorStyleDisabled, (aStyleDisabled));
+}
+
+void
+StyleSetHandle::Ptr::BeginUpdate()
+{
+  FORWARD(BeginUpdate, ());
+}
+
+nsresult
+StyleSetHandle::Ptr::EndUpdate()
+{
+  FORWARD(EndUpdate, ());
+}
+
+// resolve a style context
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ResolveStyleFor(dom::Element* aElement,
+                                     nsStyleContext* aParentContext)
+{
+  FORWARD(ResolveStyleFor, (aElement, aParentContext));
+}
+
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ResolveStyleFor(dom::Element* aElement,
+                                     nsStyleContext* aParentContext,
+                                     TreeMatchContext& aTreeMatchContext)
+{
+  FORWARD(ResolveStyleFor, (aElement, aParentContext, aTreeMatchContext));
+}
+
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ResolveStyleForNonElement(nsStyleContext* aParentContext)
+{
+  FORWARD(ResolveStyleForNonElement, (aParentContext));
+}
+
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ResolvePseudoElementStyle(dom::Element* aParentElement,
+                                               CSSPseudoElementType aType,
+                                               nsStyleContext* aParentContext,
+                                               dom::Element* aPseudoElement)
+{
+  FORWARD(ResolvePseudoElementStyle, (aParentElement, aType, aParentContext,
+                                      aPseudoElement));
+}
+
+// aFlags is an nsStyleSet flags bitfield
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ResolveAnonymousBoxStyle(nsIAtom* aPseudoTag,
+                                              nsStyleContext* aParentContext,
+                                              uint32_t aFlags)
+{
+  FORWARD(ResolveAnonymousBoxStyle, (aPseudoTag, aParentContext, aFlags));
+}
+
+// manage the set of style sheets in the style set
+nsresult
+StyleSetHandle::Ptr::AppendStyleSheet(SheetType aType, CSSStyleSheet* aSheet)
+{
+  FORWARD(AppendStyleSheet, (aType, aSheet));
+}
+
+nsresult
+StyleSetHandle::Ptr::PrependStyleSheet(SheetType aType, CSSStyleSheet* aSheet)
+{
+  FORWARD(PrependStyleSheet, (aType, aSheet));
+}
+
+nsresult
+StyleSetHandle::Ptr::RemoveStyleSheet(SheetType aType, CSSStyleSheet* aSheet)
+{
+  FORWARD(RemoveStyleSheet, (aType, aSheet));
+}
+
+nsresult
+StyleSetHandle::Ptr::ReplaceSheets(SheetType aType,
+                       const nsTArray<RefPtr<CSSStyleSheet>>& aNewSheets)
+{
+  FORWARD(ReplaceSheets, (aType, aNewSheets));
+}
+
+nsresult
+StyleSetHandle::Ptr::InsertStyleSheetBefore(SheetType aType,
+                                CSSStyleSheet* aNewSheet,
+                                CSSStyleSheet* aReferenceSheet)
+{
+  FORWARD(InsertStyleSheetBefore, (aType, aNewSheet, aReferenceSheet));
+}
+
+int32_t
+StyleSetHandle::Ptr::SheetCount(SheetType aType) const
+{
+  FORWARD(SheetCount, (aType));
+}
+
+CSSStyleSheet*
+StyleSetHandle::Ptr::StyleSheetAt(SheetType aType, int32_t aIndex) const
+{
+  FORWARD(StyleSheetAt, (aType, aIndex));
+}
+
+nsresult
+StyleSetHandle::Ptr::RemoveDocStyleSheet(CSSStyleSheet* aSheet)
+{
+  FORWARD(RemoveDocStyleSheet, (aSheet));
+}
+
+nsresult
+StyleSetHandle::Ptr::AddDocStyleSheet(CSSStyleSheet* aSheet,
+                                      nsIDocument* aDocument)
+{
+  FORWARD(AddDocStyleSheet, (aSheet, aDocument));
+}
+
+// check whether there is ::before/::after style for an element
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ProbePseudoElementStyle(dom::Element* aParentElement,
+                                             CSSPseudoElementType aType,
+                                             nsStyleContext* aParentContext)
+{
+  FORWARD(ProbePseudoElementStyle, (aParentElement, aType, aParentContext));
+}
+
+already_AddRefed<nsStyleContext>
+StyleSetHandle::Ptr::ProbePseudoElementStyle(dom::Element* aParentElement,
+                                             CSSPseudoElementType aType,
+                                             nsStyleContext* aParentContext,
+                                             TreeMatchContext& aTreeMatchContext,
+                                             dom::Element* aPseudoElement)
+{
+  FORWARD(ProbePseudoElementStyle, (aParentElement, aType, aParentContext,
+                                    aTreeMatchContext, aPseudoElement));
+}
+
+nsRestyleHint
+StyleSetHandle::Ptr::HasStateDependentStyle(dom::Element* aElement,
+                                            EventStates aStateMask)
+{
+  FORWARD(HasStateDependentStyle, (aElement, aStateMask));
+}
+
+nsRestyleHint
+StyleSetHandle::Ptr::HasStateDependentStyle(dom::Element* aElement,
+                                            CSSPseudoElementType aPseudoType,
+                                            dom::Element* aPseudoElement,
+                                            EventStates aStateMask)
+{
+  FORWARD(HasStateDependentStyle, (aElement, aPseudoType, aPseudoElement,
+                                   aStateMask));
+}
+
+} // namespace mozilla
+
+#undef FORWARD
+
+#endif // mozilla_StyleSetHandleInlines_h
diff --git a/layout/style/moz.build b/layout/style/moz.build
index 1f771b096bf5..25095e1ad5b0 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -88,9 +88,12 @@ EXPORTS.mozilla += [
     'LayerAnimationInfo.h',
     'RuleNodeCacheConditions.h',
     'RuleProcessorCache.h',
+    'ServoStyleSet.h',
     'SheetType.h',
     'StyleAnimationValue.h',
     'StyleBackendType.h',
+    'StyleSetHandle.h',
+    'StyleSetHandleInlines.h',
 ]
 
 EXPORTS.mozilla.dom += [
@@ -172,6 +175,7 @@ UNIFIED_SOURCES += [
     'nsTransitionManager.cpp',
     'RuleNodeCacheConditions.cpp',
     'RuleProcessorCache.cpp',
+    'ServoStyleSet.cpp',
     'StyleAnimationValue.cpp',
     'StyleRule.cpp',
     'SVGAttrAnimationRuleProcessor.cpp',