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 99 matching lines @@
   // is pending at a time.
   virtual void DidFinishFrame(size_t remaining_frames) = 0;
 
   // Add/Remove an observer from the source.
   // *At the moment* only a single observer can be added to the source, however
   // in the future this may be extended to allow multiple observers.
   // If making this change, please use base::ObserverList to do so.
   virtual void AddObserver(BeginFrameObserver* obs) = 0;
   virtual void RemoveObserver(BeginFrameObserver* obs) = 0;
 
+  // Tells the Source that client is ready to handle BeginFrames messages.
+  virtual void SetClientReady() = 0;
+
   // Tracing support - Recommend (but not required) to call this implementation
   // in any override.
   virtual void AsValueInto(base::debug::TracedValue* dict) const = 0;
 };
 
 // Simple mix in which implements a BeginFrameSource.
 // Implementation classes should:
 //  - Implement the pure virtual (Set)NeedsBeginFrames methods from
 //    BeginFrameSource.
 //  - Use the CallOnBeginFrame method to call to the observer(s).
 //  - Recommended (but not required) to call BeginFrameSourceMixIn::AsValueInto
 //    in their own AsValueInto implementation.
 class CC_EXPORT BeginFrameSourceMixIn : public BeginFrameSource {
  public:
   ~BeginFrameSourceMixIn() override {}
 
   // BeginFrameSource
   bool NeedsBeginFrames() const override;
   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 AddObserver(BeginFrameObserver* obs) final;
+  void RemoveObserver(BeginFrameObserver* obs) final;
+  void SetClientReady() override {}
 
   // Tracing support - Recommend (but not required) to call this implementation
   // in any override.
   void AsValueInto(base::debug::TracedValue* dict) const override;
 
  protected:
   BeginFrameSourceMixIn();
 
   // These methods should be used by subclasses to make the call to the
   // observers.
@@ skipping 118 matching lines @@
 
   base::TimeDelta minimum_interval_;
 
   BeginFrameSource* active_source_;
   std::set<BeginFrameSource*> source_list_;
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_