Bug 906643. Part 1: Add nsRefreshDriver::Add/Remove/PostRefreshObserver so we can receive notifications when a refresh has occurred, without triggering one. r=dbaron

--HG--
extra : rebase_source : fbfdd2678f4561f421fda2eb17e9e7ae8754f8d3

layout/base/nsRefreshDriver.cpp

@@ -753,9 +753,7 @@ nsRefreshDriver::AddRefreshObserver(nsARefreshObserver* aObserver,
 {
   ObserverArray& array = ArrayFor(aFlushType);
   bool success = array.AppendElement(aObserver) != nullptr;
-
   EnsureTimerStarted(false);
-
   return success;
 }
 
@@ -767,6 +765,18 @@ nsRefreshDriver::RemoveRefreshObserver(nsARefreshObserver* aObserver,
   return array.RemoveElement(aObserver);
 }
 
+void
+nsRefreshDriver::AddPostRefreshObserver(nsAPostRefreshObserver* aObserver)
+{
+  mPostRefreshObservers.AppendElement(aObserver);
+}
+
+void
+nsRefreshDriver::RemovePostRefreshObserver(nsAPostRefreshObserver* aObserver)
+{
+  mPostRefreshObservers.RemoveElement(aObserver);
+}
+
 bool
 nsRefreshDriver::AddImageRequest(imgIRequest* aRequest)
 {
@@ -1198,6 +1208,10 @@ nsRefreshDriver::Tick(int64_t aNowEpoch, TimeStamp aNowTime)
     }
 #endif
   }
+
+  for (uint32_t i = 0; i < mPostRefreshObservers.Length(); ++i) {
+    mPostRefreshObservers[i]->DidRefresh();
+  }
 }
 
 /* static */ PLDHashOperator

layout/base/nsRefreshDriver.h

@@ -26,16 +26,17 @@ class nsPresContext;
 class nsIPresShell;
 class nsIDocument;
 class imgIRequest;
+class nsIRunnable;
+
+namespace mozilla {
+class RefreshDriverTimer;
+}
 
 /**
  * An abstract base class to be implemented by callers wanting to be
  * notified at refresh times.  When nothing needs to be painted, callers
  * may not be notified.
  */
-namespace mozilla {
-    class RefreshDriverTimer;
-}
-
 class nsARefreshObserver {
 public:
   // AddRef and Release signatures that match nsISupports.  Implementors
@@ -50,6 +51,16 @@ public:
   virtual void WillRefresh(mozilla::TimeStamp aTime) = 0;
 };
 
+/**
+ * An abstract base class to be implemented by callers wanting to be notified
+ * that a refresh has occurred. Callers must ensure an observer is removed
+ * before it is destroyed.
+ */
+class nsAPostRefreshObserver {
+public:
+  virtual void DidRefresh() = 0;
+};
+
 class nsRefreshDriver MOZ_FINAL : public nsISupports {
 public:
   nsRefreshDriver(nsPresContext *aPresContext);
@@ -101,11 +112,21 @@ public:
    *
    * The refresh driver does NOT own a reference to these observers;
    * they must remove themselves before they are destroyed.
+   *
+   * The observer will be called even if there is no other activity.
    */
   bool AddRefreshObserver(nsARefreshObserver *aObserver,
-                            mozFlushType aFlushType);
+                          mozFlushType aFlushType);
   bool RemoveRefreshObserver(nsARefreshObserver *aObserver,
-                               mozFlushType aFlushType);
+                             mozFlushType aFlushType);
+
+  /**
+   * Add an observer that will be called after each refresh. The caller
+   * must remove the observer before it is deleted. This does not trigger
+   * refresh driver ticks.
+   */
+  void AddPostRefreshObserver(nsAPostRefreshObserver *aObserver);
+  void RemovePostRefreshObserver(nsAPostRefreshObserver *aObserver);
 
   /**
    * Add/Remove imgIRequest versions of observers.
@@ -295,6 +316,7 @@ private:
   nsAutoTArray<nsIPresShell*, 16> mPresShellsToInvalidateIfHidden;
   // nsTArray on purpose, because we want to be able to swap.
   nsTArray<nsIDocument*> mFrameRequestCallbackDocs;
+  nsTArray<nsAPostRefreshObserver*> mPostRefreshObservers;
 
   // Helper struct for processing image requests
   struct ImageRequestParameters {