Make CommandBuffer::Flush asynchronous, and add CommandBuffer::FlushSync with former semantics.

gpu/command_buffer/service/command_buffer_service.h

Index: gpu/command_buffer/service/command_buffer_service.h
diff --git a/gpu/command_buffer/service/command_buffer_service.h b/gpu/command_buffer/service/command_buffer_service.h
index d9be20aa128d62d320565f967114c046112977d0..94d77c38cdef147173bc4ad2a152643bfb7c3cac 100644
--- a/gpu/command_buffer/service/command_buffer_service.h
+++ b/gpu/command_buffer/service/command_buffer_service.h
@@ -28,7 +28,8 @@ class CommandBufferService : public CommandBuffer {
   virtual bool Initialize(int32 size);
   virtual Buffer GetRingBuffer();
   virtual State GetState();
-  virtual State Flush(int32 put_offset);
+  virtual void Flush(int32 put_offset);
+  virtual State FlushSync(int32 put_offset);
   virtual void SetGetOffset(int32 get_offset);
   virtual int32 CreateTransferBuffer(size_t size);
   virtual void DestroyTransferBuffer(int32 id);