cc: Make BackToBackBeginFrameSource a SyntheticBeginFrameSource.

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 575ab06beb450555065d2801b7f388c3b4180bdc..1f5aabb6fe271a8655a768e345a16ec547dcd09b 100644
--- a/cc/scheduler/begin_frame_source.h
+++ b/cc/scheduler/begin_frame_source.h
@@ -131,7 +131,7 @@ class CC_EXPORT BeginFrameSourceBase : public BeginFrameSource {
  public:
   ~BeginFrameSourceBase() override;
 
-  // BeginFrameSource
+  // BeginFrameSource implementation.
   void DidFinishFrame(BeginFrameObserver* obs,
                       size_t remaining_frames) override {}
   void AddObserver(BeginFrameObserver* obs) override;
@@ -145,7 +145,7 @@ class CC_EXPORT BeginFrameSourceBase : public BeginFrameSource {
   void CallOnBeginFrame(const BeginFrameArgs& args);
   void SetBeginFrameSourcePaused(bool paused);
 
-  // This notifies that the subclass that it must turn on or off its mechnanism
+  // This notifies the subclass that it must turn on or off its mechnanism
   // for producing BeginFrames.
   virtual void OnNeedsBeginFramesChanged(bool needs_begin_frames) {}
 
@@ -158,43 +158,11 @@ class CC_EXPORT BeginFrameSourceBase : public BeginFrameSource {
   DISALLOW_COPY_AND_ASSIGN(BeginFrameSourceBase);
 };
 
-// A frame source which calls BeginFrame (at the next possible time) as soon as
-// remaining frames reaches zero.
-class CC_EXPORT BackToBackBeginFrameSource : public BeginFrameSourceBase {
- public:
-  explicit BackToBackBeginFrameSource(
-      base::SingleThreadTaskRunner* task_runner);
-  ~BackToBackBeginFrameSource() override;
-
-  // BeginFrameSource
-  void AddObserver(BeginFrameObserver* obs) override;
-  void RemoveObserver(BeginFrameObserver* obs) override;
-  void DidFinishFrame(BeginFrameObserver* obs,
-                      size_t remaining_frames) override;
-
- protected:
-  virtual base::TimeTicks Now();  // Now overridable for testing
-
-  base::SingleThreadTaskRunner* task_runner_;
-  base::CancelableClosure begin_frame_task_;
-  std::set<BeginFrameObserver*> pending_begin_frame_observers_;
-
-  void PostPendingBeginFramesTask();
-  void SendPendingBeginFrames();
-
- private:
-  base::WeakPtrFactory<BackToBackBeginFrameSource> weak_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(BackToBackBeginFrameSource);
-};
-
 // A frame source which is locked to an external parameters provides from a
 // vsync source and generates BeginFrameArgs for it.
 class CC_EXPORT SyntheticBeginFrameSource : public BeginFrameSourceBase,
                                             public DelayBasedTimeSourceClient {
  public:
-  explicit SyntheticBeginFrameSource(base::SingleThreadTaskRunner* task_runner,
-                                     base::TimeDelta initial_vsync_interval);
   explicit SyntheticBeginFrameSource(
       std::unique_ptr<DelayBasedTimeSource> time_source);
   ~SyntheticBeginFrameSource() override;
@@ -204,25 +172,49 @@ class CC_EXPORT SyntheticBeginFrameSource : public BeginFrameSourceBase,
   // This overrides any past or future interval from updating vsync parameters.
   void SetAuthoritativeVSyncInterval(base::TimeDelta interval);
 
-  // BeginFrameSourceBase
+  // BeginFrameSourceBase overrides.
   void AddObserver(BeginFrameObserver* obs) override;
+  void RemoveObserver(BeginFrameObserver* obs) override;
   void OnNeedsBeginFramesChanged(bool needs_begin_frames) override;
+  void DidFinishFrame(BeginFrameObserver* obs,
+                      size_t remaining_frames) override;
 
   // DelayBasedTimeSourceClient
   void OnTimerTick() override;
 
+  // When unthrottled, BeginFrames will be generates as fast as previous frames
+  // finish for each observer.
+  void SetUnthrottled(bool unthrottled);
+
  protected:
   BeginFrameArgs CreateBeginFrameArgs(base::TimeTicks frame_time,
                                       BeginFrameArgs::BeginFrameArgsType type);
 
   std::unique_ptr<DelayBasedTimeSource> time_source_;
   base::TimeTicks last_timebase_;
+  base::TimeDelta last_interval_;
   base::TimeDelta authoritative_interval_;
 
+  bool unthrottled_ = false;
+  bool needs_unthrottled_tick_ = false;
+  std::set<BeginFrameObserver*> frame_finished_observers_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SyntheticBeginFrameSource);
 };
 
+// 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:
+  explicit BackToBackBeginFrameSource(
+      base::SingleThreadTaskRunner* task_runner);
+  ~BackToBackBeginFrameSource() override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BackToBackBeginFrameSource);
+};
+
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_