Plumb GpuSwapBuffers completion from Mus GPU thread to WS thread

components/mus/surfaces/surfaces_context_provider.h

Index: components/mus/surfaces/surfaces_context_provider.h
diff --git a/components/mus/surfaces/surfaces_context_provider.h b/components/mus/surfaces/surfaces_context_provider.h
index 520ff1388b36a4a6aab6cab4ca79c34ae7355a81..3255cf04cb9c85b99ec961dcac3bc22146d73276 100644
--- a/components/mus/surfaces/surfaces_context_provider.h
+++ b/components/mus/surfaces/surfaces_context_provider.h
@@ -13,6 +13,7 @@
 #include "cc/output/context_provider.h"
 #include "components/mus/gles2/command_buffer_local_client.h"
 #include "ui/gfx/native_widget_types.h"
+#include "ui/gl/gl_surface.h"
 
 namespace gpu {
 
@@ -54,6 +55,10 @@ class SurfacesContextProvider : public cc::ContextProvider,
   void SetupLock() override;
   base::Lock* GetLock() override;
 
+  // SurfacesContextProvider API.
+  void SetSwapBuffersCompletionCallback(
+      gfx::GLSurface::SwapCompletionCallback callback);
+
  protected:
   friend class base::RefCountedThreadSafe<SurfacesContextProvider>;
   ~SurfacesContextProvider() override;
@@ -62,6 +67,7 @@ class SurfacesContextProvider : public cc::ContextProvider,
   // CommandBufferLocalClient:
   void UpdateVSyncParameters(int64_t timebase, int64_t interval) override;
   void DidLoseContext() override;
+  void GpuCompletedSwapBuffers(gfx::SwapResult result) override;
 
   // From GLES2Context:
   // Initialized in BindToCurrentThread.
@@ -76,6 +82,8 @@ class SurfacesContextProvider : public cc::ContextProvider,
   gfx::AcceleratedWidget widget_;
   CommandBufferLocal* command_buffer_local_;
 
+  gfx::GLSurface::SwapCompletionCallback swap_buffers_completion_callback_;
+
   base::Lock context_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfacesContextProvider);