cc: Create ProxyBeginFrameSource

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 299db8e31d9b36176ffc98c17092ccc251110fd3..8afeafa3d20d7d4e74f8b37dbe0dbd718479b445 100644
--- a/cc/scheduler/begin_frame_source.h
+++ b/cc/scheduler/begin_frame_source.h
@@ -166,6 +166,44 @@ class CC_EXPORT BeginFrameSourceMixIn : public BeginFrameSource {
   bool inside_as_value_into_;
 };
 
+class CC_EXPORT ProxyBeginFrameSource : public BeginFrameSource {

[mithro-old, 2015/03/23 11:32:17]

If I understand correctly, this just takes a message from a BeginFrameSource and
forwards it to multiple observers?

[simonhong, 2015/03/23 11:46:39]

Yes, right.

+ public:
+  class Delegate {
+   public:
+    virtual void SetChildrenNeedBeginFrames(bool needs_begin_frames) = 0;
+  };
+
+  ProxyBeginFrameSource();
+  ~ProxyBeginFrameSource() override;
+
+  // BeginFrameSource
+  bool NeedsBeginFrames() const override;
+  // SetNeedsBeginFrames() is not used for now.
+  // Instead, turning BeginFrame on/off is controlled by Add/RemoveObserver.

[mithro-old, 2015/03/23 11:32:17]

I think this violates the BeginFrameSource interface, if
SetNeedsBeginFrames(false) is called, we shouldn't be sending any more
BeginFrames?

Can you explain why you are controlling this via Observers rather than the
normal method?

[simonhong, 2015/03/23 11:46:39]

This is special login for ProxyBeginFrameSource.
We only can stop sending BeginFrame if there is no observer.
Of course, login in Add/RemoveObserver can be moved into SetNeedsBeginFrames().

+  void SetNeedsBeginFrames(bool needs_begin_frames) override {}
+  void DidFinishFrame(size_t remaining_frames) override {}
+  void AddObserver(BeginFrameObserver* obs) override;
+  void RemoveObserver(BeginFrameObserver* obs) override;
+  void SetClientReady() override {}
+  void AsValueInto(base::debug::TracedValue* dict) const override;
+
+  void set_delegate(Delegate* delegate) {

[mithro-old, 2015/03/23 11:32:17]

Why is this set_delegate rather than SetDelegate?

[simonhong, 2015/03/23 11:46:39]

As I know, this style is used for just get/set method.
Am I wrong? :)

+    delegate_ = delegate;
+  }
+
+  // virtual for testing.
+  virtual void BeginFrames(const BeginFrameArgs& args);
+
+ private:
+  Delegate* delegate_;  // Not owned.
+  // Used to send to any new BeginFrameObserver immediately.
+  BeginFrameArgs missed_begin_frame_args_;
+  ObserverList<BeginFrameObserver> observer_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProxyBeginFrameSource);
+};
+
+
 // A frame source which calls BeginFrame (at the next possible time) as soon as
 // remaining frames reaches zero.
 class CC_EXPORT BackToBackBeginFrameSource : public BeginFrameSourceMixIn {