--- a/layout/style/ServoStyleSet.cpp
+++ b/layout/style/ServoStyleSet.cpp
@@ -864,16 +864,23 @@ ServoStyleSet::ResolveStyleLazily(Elemen
     computedValues =
       Servo_ResolveStyleLazily(aElement, aPseudoTag, mRawSet.get()).Consume();
   }
   sInServoTraversal = false;
 
   return computedValues.forget();
 }
 
+already_AddRefed<ServoComputedValues>
+ServoStyleSet::ResolveServoStyle(Element* aElement, nsIAtom* aPseudoTag)
+{
+  PreTraverseSync();
+  return ResolveStyleLazily(aElement, aPseudoTag);
+}
+
 bool
 ServoStyleSet::AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray)
 {
   Servo_StyleSet_GetFontFaceRules(mRawSet.get(), &aArray);
   return true;
 }
 
 bool ServoStyleSet::sInServoTraversal = false;

--- a/layout/style/ServoStyleSet.h
+++ b/layout/style/ServoStyleSet.h
@@ -266,16 +266,24 @@ public:
   void RebuildData();
 
   /**
    * Resolve style for the given element, and return it as a
    * ServoComputedValues, not an nsStyleContext.
    */
   already_AddRefed<ServoComputedValues> ResolveServoStyleWithoutSyncUpData(dom::Element* aElement);
 
+  /**
+   * Resolve style for the given (pseudo-)element and pseudo information,
+   * and it will call PreTraverseSync() first.
+   */
+  already_AddRefed<ServoComputedValues>
+  ResolveServoStyle(dom::Element* aElement,
+                                       nsIAtom* aPseudoTag);
+
   bool FillKeyframesForName(const nsString& aName,
                             const nsTimingFunction& aTimingFunction,
                             const ServoComputedValues* aComputedValues,
                             nsTArray<Keyframe>& aKeyframes);
 
   nsTArray<ComputedKeyframeValues>
   GetComputedKeyframeValuesFor(const nsTArray<Keyframe>& aKeyframes,
                                dom::Element* aElement,