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

gpu/pgl/command_buffer_pepper.h

Index: gpu/pgl/command_buffer_pepper.h
diff --git a/gpu/pgl/command_buffer_pepper.h b/gpu/pgl/command_buffer_pepper.h
index 5d11d981eacf18f7292c19ea550ac3f580795323..fe80625d54c94ce771d39cfe9ab58d75d9e9083a 100644
--- a/gpu/pgl/command_buffer_pepper.h
+++ b/gpu/pgl/command_buffer_pepper.h
@@ -29,7 +29,8 @@ class CommandBufferPepper : public gpu::CommandBuffer {
   virtual bool Initialize(int32 size);
   virtual gpu::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);