cc: Send all begin frames using a PostTask.

cc/scheduler/begin_frame_source.h

Index: cc/scheduler/begin_frame_source.h
diff --git a/cc/scheduler/begin_frame_source.h b/cc/scheduler/begin_frame_source.h
index 0a8a51f08d7c911d6c1594b1623ae74ad5a9fe43..114727028cf6f9b2e2aee5abd7790db1e439b2f6 100644
--- a/cc/scheduler/begin_frame_source.h
+++ b/cc/scheduler/begin_frame_source.h
@@ -136,11 +136,13 @@ class CC_EXPORT SyntheticBeginFrameSource : public BeginFrameSource {
 
 // A frame source which calls BeginFrame (at the next possible time) as soon as
 // remaining frames reaches zero.
-class CC_EXPORT BackToBackBeginFrameSource : public SyntheticBeginFrameSource,
-                                             public DelayBasedTimeSourceClient {
+class CC_EXPORT BackToBackBeginFrameSource : public SyntheticBeginFrameSource {
  public:
   explicit BackToBackBeginFrameSource(
-      std::unique_ptr<DelayBasedTimeSource> time_source);
+      base::SingleThreadTaskRunner* task_runner);
+  // For testing.

[danakj, 2016/07/13 21:00:59]

Can we avoid reintroducing for-testing constructors?

+  BackToBackBeginFrameSource(base::SingleThreadTaskRunner* task_runner,
+                             base::TickClock* clock);
   ~BackToBackBeginFrameSource() override;
 
   // BeginFrameSource implementation.
@@ -154,13 +156,14 @@ class CC_EXPORT BackToBackBeginFrameSource : public SyntheticBeginFrameSource,
                                base::TimeDelta interval) override {}
   void SetAuthoritativeVSyncInterval(base::TimeDelta interval) override {}
 
-  // DelayBasedTimeSourceClient implementation.
-  void OnTimerTick() override;
-
  private:
-  std::unique_ptr<DelayBasedTimeSource> time_source_;
+  void SendBeginFrame();
+
+  base::SingleThreadTaskRunner* task_runner_;
+  base::TickClock* clock_;
+  base::CancelableClosure begin_frame_callback_;
   std::unordered_set<BeginFrameObserver*> observers_;
-  std::unordered_set<BeginFrameObserver*> pending_begin_frame_observers_;
+  std::unordered_set<BeginFrameObserver*> pending_observers_;
   base::WeakPtrFactory<BackToBackBeginFrameSource> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BackToBackBeginFrameSource);
@@ -172,7 +175,10 @@ class CC_EXPORT DelayBasedBeginFrameSource : public SyntheticBeginFrameSource,
                                              public DelayBasedTimeSourceClient {
  public:
   explicit DelayBasedBeginFrameSource(
-      std::unique_ptr<DelayBasedTimeSource> time_source);
+      base::SingleThreadTaskRunner* task_runner);
+  // For testing.
+  DelayBasedBeginFrameSource(base::SingleThreadTaskRunner* task_runner,
+                             base::TickClock* clock);
   ~DelayBasedBeginFrameSource() override;
 
   // BeginFrameSource implementation.
@@ -192,11 +198,16 @@ class CC_EXPORT DelayBasedBeginFrameSource : public SyntheticBeginFrameSource,
  private:
   BeginFrameArgs CreateBeginFrameArgs(base::TimeTicks frame_time,
                                       BeginFrameArgs::BeginFrameArgsType type);
+  void SendMissedBeginFrame();
 
   std::unique_ptr<DelayBasedTimeSource> time_source_;
+  base::SingleThreadTaskRunner* task_runner_;
+  base::CancelableClosure missed_frame_callback_;
   std::unordered_set<BeginFrameObserver*> observers_;
+  std::unordered_set<BeginFrameObserver*> missed_frame_observers_;
   base::TimeTicks last_timebase_;
   base::TimeDelta authoritative_interval_;
+  base::WeakPtrFactory<DelayBasedBeginFrameSource> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DelayBasedBeginFrameSource);
 };