cc: Make separate interface for BeginFrame ipc from OutputSurface

cc/scheduler/begin_frame_source.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_
 #define CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_
 
 #include <set>
 #include <string>
 
@@ skipping 144 matching lines @@
   // needs_begin_frames change.
   virtual void OnNeedsBeginFramesChange(bool needs_begin_frames) {}
 
   BeginFrameObserver* observer_;
   bool needs_begin_frames_;
 
  private:
   bool inside_as_value_into_;
 };
 
+// A frame source that delivers BeginFrame from outside of CC layer.

[danakj, 2014/10/10 16:03:35]

from outside of cc.

[simonhong, 2014/10/15 01:04:21]

Done.

+class CC_EXPORT ExternalBeginFrameSource : public BeginFrameSourceMixIn {

[danakj, 2014/10/10 16:03:35]

This should inherit from BeginFrameSource (or why not just add SetClientReady to
BeginFrameSource and use that?)

The MixIn has concrete implementations, it should inherit from an abstract
class, not vice versa. And users of ExternalBFS shouldn't care that the MixIn
class is implementing parts of the interface.

[simonhong, 2014/10/15 01:04:21]

I think ExternalBeginFrameSource should have a different specs such as
ref-counted and non-thread safe object because it would be used to request
BeginFrame from outside of cc(in browser-side scheduler with unified
BeginFrame).
So, I made it as a concrete class for base class.

[danakj, 2014/10/15 06:49:49]

So you have a use case for why it would need to be ref counted?

+ public:
+  virtual ~ExternalBeginFrameSource() {}
+
+  // Tells the Source that client is ready to handle external BeginFrames.
+  virtual void SetClientReady() = 0;
+};
+
 // A frame source which calls BeginFrame (at the next possible time) as soon as
 // remaining frames reaches zero.
 class CC_EXPORT BackToBackBeginFrameSource : public BeginFrameSourceMixIn {
  public:
   static scoped_ptr<BackToBackBeginFrameSource> Create(
       base::SingleThreadTaskRunner* task_runner);
   virtual ~BackToBackBeginFrameSource();
 
   // BeginFrameSource
   virtual void DidFinishFrame(size_t remaining_frames) override;
@@ skipping 96 matching lines @@
 
   base::TimeDelta minimum_interval_;
 
   BeginFrameSource* active_source_;
   std::set<BeginFrameSource*> source_list_;
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_