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

gpu/command_buffer/client/gles2_implementation_unittest.cc

Index: gpu/command_buffer/client/gles2_implementation_unittest.cc
diff --git a/gpu/command_buffer/client/gles2_implementation_unittest.cc b/gpu/command_buffer/client/gles2_implementation_unittest.cc
index d431851e503d73b1234f7f03f80cc8e78c70d1cd..89d9bd3d5440e79c413a12e0d39cd984c58534cf 100644
--- a/gpu/command_buffer/client/gles2_implementation_unittest.cc
+++ b/gpu/command_buffer/client/gles2_implementation_unittest.cc
@@ -37,7 +37,11 @@ class GLES2MockCommandBufferHelper : public CommandBuffer {
     return state_;
   }
 
-  virtual State Flush(int32 put_offset) {
+  virtual void Flush(int32 put_offset) {
+    FlushSync(put_offset);
+  }
+
+  virtual State FlushSync(int32 put_offset) {
     state_.put_offset = put_offset;
     state_.get_offset = put_offset;
     OnFlush(transfer_buffer_buffer_.ptr);