Added GPU process "echo" IPC message.

gpu/command_buffer/service/gpu_scheduler_mac.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gpu_scheduler.h"
 #include "ui/gfx/gl/gl_context.h"
 #include "ui/gfx/gl/gl_share_group.h"
 #include "ui/gfx/gl/gl_surface.h"
 
 using ::base::SharedMemory;
@@ skipping 102 matching lines @@
   // will attempt to finish all GL commands, it will busy-wait on the GPU
   // process until the command queue is empty. If a paint is pending, the GPU
   // process won't process any GL commands until the browser sends a paint ack,
   // but since the browser window is already closed, it will never arrive.
   // To break this infinite loop, the browser tells the GPU process that the
   // surface became invalid, which causes the GPU process to not wait for paint
   // acks.
   surface_.reset();
 }
 
+void GpuScheduler::SetSwapBuffersCallback(
+    Callback0::Type* callback) {
+  wrapped_swap_buffers_callback_.reset(callback);
+  decoder_->SetSwapBuffersCallback(
+      NewCallback(this,
+                  &GpuScheduler::WillSwapBuffers));
+}
+
 void GpuScheduler::WillSwapBuffers() {
   DCHECK(decoder_.get());
   DCHECK(decoder_->GetGLContext());
   DCHECK(decoder_->GetGLContext()->IsCurrent(decoder_->GetGLSurface()));
 
   ++swap_buffers_count_;
 
   if (surface_.get()) {
     surface_->SwapBuffers();
   }
 
   if (wrapped_swap_buffers_callback_.get()) {
     wrapped_swap_buffers_callback_->Run();
   }
 }
 
 }  // namespace gpu