diff --git a/layout/style/ServoBindingList.h b/layout/style/ServoBindingList.h
index 66aa1e497353..19f4b57f18bb 100644
--- a/layout/style/ServoBindingList.h
+++ b/layout/style/ServoBindingList.h
@@ -647,6 +647,14 @@ SERVO_BINDING_FUNC(Servo_StyleSet_GetBaseComputedValuesForElement,
                    ServoStyleContextBorrowed existing_style,
                    const mozilla::ServoElementSnapshotTable* snapshots,
                    mozilla::CSSPseudoElementType pseudo_type)
+// Returns computed values for the given element by adding an animation value.
+SERVO_BINDING_FUNC(Servo_StyleSet_GetComputedValuesByAddingAnimation,
+                   ServoStyleContextStrong,
+                   RawServoStyleSetBorrowed set,
+                   RawGeckoElementBorrowed element,
+                   ServoStyleContextBorrowed existing_style,
+                   const mozilla::ServoElementSnapshotTable* snapshots,
+                   RawServoAnimationValueBorrowed animation)
 
 // For canvas font.
 SERVO_BINDING_FUNC(Servo_SerializeFontValueForCanvas, void,
diff --git a/layout/style/ServoStyleSet.cpp b/layout/style/ServoStyleSet.cpp
index 7dd78abc7b5e..4089dfddb19f 100644
--- a/layout/style/ServoStyleSet.cpp
+++ b/layout/style/ServoStyleSet.cpp
@@ -1239,6 +1239,25 @@ ServoStyleSet::GetBaseContextForElement(
                                                         aPseudoType).Consume();
 }
 
+already_AddRefed<ServoStyleContext>
+ServoStyleSet::ResolveServoStyleByAddingAnimation(
+  Element* aElement,
+  const ServoStyleContext* aStyle,
+  RawServoAnimationValue* aAnimationValue)
+{
+  MOZ_RELEASE_ASSERT(!aElement->OwnerDoc()->GetBFCacheEntry(),
+                     "ResolveServoStyleByAddingAniamtion does not support "
+                     "documents in the bfcache");
+
+  AutoClearStaleData guard(aElement);
+  return Servo_StyleSet_GetComputedValuesByAddingAnimation(
+    mRawSet.get(),
+    aElement,
+    aStyle,
+    &Snapshots(),
+    aAnimationValue).Consume();
+}
+
 already_AddRefed<RawServoAnimationValue>
 ServoStyleSet::ComputeAnimationValue(
   Element* aElement,
diff --git a/layout/style/ServoStyleSet.h b/layout/style/ServoStyleSet.h
index 7fcded6f1ea8..cf4dc903c35f 100644
--- a/layout/style/ServoStyleSet.h
+++ b/layout/style/ServoStyleSet.h
@@ -392,6 +392,20 @@ public:
                            CSSPseudoElementType aPseudoType,
                            const ServoStyleContext* aStyle);
 
+  // Get a style context that represents |aStyle|, but as though
+  // it additionally matched the rules of the newly added |aAnimaitonaValue|.
+  // We use this function to temporarily generate a ServoStyleContext for
+  // calculating the cumulative change hints.
+  // This must hold:
+  //   The additional rules must be appropriate for the transition
+  //   level of the cascade, which is the highest level of the cascade.
+  //   (This is the case for one current caller, the cover rule used
+  //   for CSS transitions.)
+  // Note: |aElement| should be the generated element if it is pseudo.
+  already_AddRefed<ServoStyleContext>
+  ResolveServoStyleByAddingAnimation(dom::Element* aElement,
+                                     const ServoStyleContext* aStyle,
+                                     RawServoAnimationValue* aAnimationValue);
   /**
    * Resolve style for a given declaration block with/without the parent style.
    * If the parent style is not specified, the document default computed values