Bug 1203766 - Part 4: Add a "restyle generation" counter, which increments whenever we process pending restyles. r=bzbarsky

layout/base/RestyleManager.cpp

@@ -83,6 +83,7 @@ RestyleManager::RestyleManager(nsPresContext* aPresContext)
   , mInStyleRefresh(false)
   , mSkipAnimationRules(false)
   , mHavePendingNonAnimationRestyles(false)
+  , mRestyleGeneration(1)
   , mHoverGeneration(0)
   , mRebuildAllExtraHint(nsChangeHint(0))
   , mRebuildAllRestyleHint(nsRestyleHint(0))

layout/base/RestyleManager.h

@@ -91,6 +91,10 @@ public:
                         int32_t  aModType,
                         const nsAttrValue* aOldValue);
 
+  // Get an integer that increments every time we process pending restyles.
+  // The value is never 0.
+  uint32_t GetRestyleGeneration() const { return mRestyleGeneration; }
+
   // Get an integer that increments every time there is a style change
   // as a result of a change to the :hover content state.
   uint32_t GetHoverGeneration() const { return mHoverGeneration; }
@@ -519,6 +523,12 @@ private:
     // Fast-path the common case (esp. for the animation restyle
     // tracker) of not having anything to do.
     if (aRestyleTracker.Count() || ShouldStartRebuildAllFor(aRestyleTracker)) {
+      if (++mRestyleGeneration == 0) {
+        // Keep mRestyleGeneration from being 0, since that's what
+        // nsPresContext::GetRestyleGeneration returns when it no
+        // longer has a RestyleManager.
+        ++mRestyleGeneration;
+      }
       aRestyleTracker.DoProcessRestyles();
     }
   }
@@ -539,6 +549,7 @@ private:
   bool mSkipAnimationRules : 1;
   bool mHavePendingNonAnimationRestyles : 1;
 
+  uint32_t mRestyleGeneration;
   uint32_t mHoverGeneration;
   nsChangeHint mRebuildAllExtraHint;
   nsRestyleHint mRebuildAllRestyleHint;

layout/base/nsPresContext.cpp

@@ -2844,6 +2844,15 @@ nsPresContext::IsDeviceSizePageSize()
   return isDeviceSizePageSize;
 }
 
+uint64_t
+nsPresContext::GetRestyleGeneration() const
+{
+  if (!mRestyleManager) {
+    return 0;
+  }
+  return mRestyleManager->GetRestyleGeneration();
+}
+
 nsRootPresContext::nsRootPresContext(nsIDocument* aDocument,
                                      nsPresContextType aType)
   : nsPresContext(aDocument, aType),

layout/base/nsPresContext.h

@@ -915,6 +915,11 @@ public:
     mAllInvalidated = false;
   }
 
+  /**
+   * Returns the RestyleManager's restyle generation counter.
+   */
+  uint64_t GetRestyleGeneration() const;
+
   /**
    * Returns whether there are any pending restyles or reflows.
    */