Let every "accelerated IO surface swapped" message have an identifier of the surface.

gpu/command_buffer/service/gpu_processor.h

Index: gpu/command_buffer/service/gpu_processor.h
diff --git a/gpu/command_buffer/service/gpu_processor.h b/gpu/command_buffer/service/gpu_processor.h
index 79d9e73e063807bf1453b32524b28a1029f49874..986ab03960c60ad5a129e168e7690c8cade79ed2 100644
--- a/gpu/command_buffer/service/gpu_processor.h
+++ b/gpu/command_buffer/service/gpu_processor.h
@@ -83,6 +83,8 @@ class GPUProcessor : public CommandBufferEngine {
   virtual void SetTransportDIBAllocAndFree(
       Callback2<size_t, TransportDIB::Handle*>::Type* allocator,
       Callback1<TransportDIB::Id>::Type* deallocator);
+  // Returns the id of the current IOSurface, or 0.
+  virtual uint64 GetSurfaceId();
 #endif
 
   // Sets a callback which is called when a SwapBuffers command is processed.