Bug 1373725 - Trigger a rule tree gc at the end of DoProcessPendingRestyles. r=emilio

MozReview-Commit-ID: W2lkQohudA

layout/base/ServoRestyleManager.cpp

@@ -680,6 +680,10 @@ ServoRestyleManager::DoProcessPendingRestyles(TraversalRestyleBehavior
   mRestyleForCSSRuleChanges = false;
   mInStyleRefresh = false;
 
+  // Now that everything has settled, see if we have enough free rule nodes in
+  // the tree to warrant sweeping them.
+  styleSet->MaybeGCRuleTree();
+
   // Note: We are in the scope of |animationsWithDestroyedFrame|, so
   //       |mAnimationsWithDestroyedFrame| is still valid.
   MOZ_ASSERT(mAnimationsWithDestroyedFrame);

layout/style/ServoBindingList.h

@@ -518,6 +518,10 @@ SERVO_BINDING_FUNC(Servo_TraverseSubtree,
 // Assert that the tree has no pending or unconsumed restyles.
 SERVO_BINDING_FUNC(Servo_AssertTreeIsClean, void, RawGeckoElementBorrowed root)
 
+// Checks whether the rule tree has crossed its threshold for unused rule nodes,
+// and if so, frees them.
+SERVO_BINDING_FUNC(Servo_MaybeGCRuleTree, void, RawServoStyleSetBorrowed set)
+
 // Returns computed values for the given element without any animations rules.
 SERVO_BINDING_FUNC(Servo_StyleSet_GetBaseComputedValuesForElement,
                    ServoComputedValuesStrong,

layout/style/ServoStyleSet.cpp

@@ -1290,6 +1290,13 @@ ServoStyleSet::UpdateStylist()
   mStylistState = StylistState::NotDirty;
 }
 
+void
+ServoStyleSet::MaybeGCRuleTree()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  Servo_MaybeGCRuleTree(mRawSet.get());
+}
+
 void
 ServoStyleSet::PrependSheetOfType(SheetType aType,
                                   ServoStyleSheet* aSheet)

layout/style/ServoStyleSet.h

@@ -341,6 +341,12 @@ public:
     }
   }
 
+  /**
+   * Checks whether the rule tree has crossed its threshold for unused nodes,
+   * and if so, frees them.
+   */
+  void MaybeGCRuleTree();
+
 #ifdef DEBUG
   void AssertTreeIsClean();
 #else