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

gpu/command_buffer/service/gpu_processor_mac.cc

Index: gpu/command_buffer/service/gpu_processor_mac.cc
diff --git a/gpu/command_buffer/service/gpu_processor_mac.cc b/gpu/command_buffer/service/gpu_processor_mac.cc
index 17dee69e0621e7b076794d97411f5f4021d01512..99721e9bbe5cb830f509f55e663fd7e50ada0020 100644
--- a/gpu/command_buffer/service/gpu_processor_mac.cc
+++ b/gpu/command_buffer/service/gpu_processor_mac.cc
@@ -93,6 +93,12 @@ void GPUProcessor::SetTransportDIBAllocAndFree(
   surface_->SetTransportDIBAllocAndFree(allocator, deallocator);
 }
 
+uint64 GPUProcessor::GetSurfaceId() {
+  if (!surface_.get())
+    return 0;
+  return surface_->GetSurfaceId();
+}
+
 void GPUProcessor::WillSwapBuffers() {
   DCHECK(decoder_.get());
   DCHECK(decoder_->GetGLContext());