Plumb GpuSwapBuffers completion from Mus GPU thread to WS thread

components/mus/gles2/command_buffer_local_client.h

Index: components/mus/gles2/command_buffer_local_client.h
diff --git a/components/mus/gles2/command_buffer_local_client.h b/components/mus/gles2/command_buffer_local_client.h
index f4b3cb43814c7b46647c5bda6131308615a7c0bf..4999f7e4b3438a4e7d2e0cf4fb35f7c4408dff2d 100644
--- a/components/mus/gles2/command_buffer_local_client.h
+++ b/components/mus/gles2/command_buffer_local_client.h
@@ -7,12 +7,15 @@
 
 #include <stdint.h>
 
+#include "ui/gfx/swap_result.h"
+
 namespace mus {
 
 class CommandBufferLocalClient {
  public:
   virtual void UpdateVSyncParameters(int64_t timebase, int64_t interval) = 0;
   virtual void DidLoseContext() = 0;
+  virtual void GpuCompletedSwapBuffers(gfx::SwapResult result) = 0;
 
  protected:
   virtual ~CommandBufferLocalClient() {}