Bug 1422528: Inline and make stylo take the rare path for GetClasses directly. r=bz

Servo already checks MayHaveClass. This should improve Gecko performance, too.

MozReview-Commit-ID: KpVOVsKh6pe

--HG--
extra : rebase_source : b0384546b1430915a18536b6ee8b29a936599873

dom/base/Element.cpp

@@ -205,18 +205,10 @@ nsIContent::DoGetID() const
 }
 
 const nsAttrValue*
-Element::DoGetClasses() const
+Element::GetSVGAnimatedClass() const
 {
-  MOZ_ASSERT(MayHaveClass(), "Unexpected call");
-  if (IsSVGElement()) {
-    const nsAttrValue* animClass =
-      static_cast<const nsSVGElement*>(this)->GetAnimatedClassName();
-    if (animClass) {
-      return animClass;
-    }
-  }
-
-  return GetParsedAttr(nsGkAtoms::_class);
+  MOZ_ASSERT(MayHaveClass() && IsSVGElement(), "Unexpected call");
+  return static_cast<const nsSVGElement*>(this)->GetAnimatedClassName();
 }
 
 NS_IMETHODIMP

dom/base/Element.h

@@ -900,6 +900,25 @@ public:
     return nullptr;
   }
 
+  /**
+   * Hook for implementing GetClasses. This should only be called if the
+   * ElementMayHaveClass flag is set.
+   *
+   * Public only because Servo needs to call it too, and it ensures the
+   * precondition before calling this.
+   */
+  const nsAttrValue* DoGetClasses() const
+  {
+    MOZ_ASSERT(MayHaveClass(), "Unexpected call");
+    if (IsSVGElement()) {
+      if (const nsAttrValue* value = GetSVGAnimatedClass()) {
+        return value;
+      }
+    }
+
+    return GetParsedAttr(nsGkAtoms::_class);
+  }
+
 #ifdef DEBUG
   virtual void List(FILE* out = stdout, int32_t aIndent = 0) const override
   {
@@ -1900,10 +1919,9 @@ protected:
 
 private:
   /**
-   * Hook for implementing GetClasses.  This is guaranteed to only be
-   * called if the NODE_MAY_HAVE_CLASS flag is set.
+   * Slow path for DoGetClasses, this should only be called for SVG elements.
    */
-  const nsAttrValue* DoGetClasses() const;
+  const nsAttrValue* GetSVGAnimatedClass() const;
 
   /**
    * Get this element's client area rect in app units.

layout/style/ServoBindings.cpp

@@ -1059,7 +1059,7 @@ template <typename Implementor>
 static uint32_t
 ClassOrClassList(Implementor* aElement, nsAtom** aClass, nsAtom*** aClassList)
 {
-  const nsAttrValue* attr = aElement->GetClasses();
+  const nsAttrValue* attr = aElement->DoGetClasses();
   if (!attr) {
     return 0;
   }

layout/style/ServoElementSnapshot.h

@@ -151,7 +151,7 @@ public:
     return nullptr;
   }
 
-  const nsAttrValue* GetClasses() const
+  const nsAttrValue* DoGetClasses() const
   {
     MOZ_ASSERT(HasAttrs());
     return &mClass;