Delay UpdateRect until the SwapBuffers callback when accelerated compositing is on.

content/browser/renderer_host/render_widget_host_unittest.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 "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/shared_memory.h"
 #include "base/timer.h"
 #include "content/browser/browser_thread_impl.h"
 #include "content/browser/renderer_host/backing_store.h"
@@ skipping 78 matching lines @@
 
   if (!current_update_buf_)
     current_update_buf_ = TransportDIB::Create(pixel_size, 0);
   params->bitmap = current_update_buf_->id();
   params->bitmap_rect = gfx::Rect(0, 0, w, h);
   params->dx = 0;
   params->dy = 0;
   params->copy_rects.push_back(params->bitmap_rect);
   params->view_size = gfx::Size(w, h);
   params->flags = update_msg_reply_flags_;
+  params->needs_ack = true;
 }
 
 bool RenderWidgetHostProcess::WaitForUpdateMsg(int render_widget_id,
                                                const base::TimeDelta& max_delay,
                                                IPC::Message* msg) {
   if (!update_msg_should_reply_)
     return false;
 
   // Construct a fake update reply.
   ViewHostMsg_UpdateRect_Params params;
@@ skipping 631 matching lines @@
   // Start it again to ensure it still works.
   EXPECT_FALSE(host_->unresponsive_timer_fired());
   host_->StartHangMonitorTimeout(TimeDelta::FromMilliseconds(10));
 
   // Wait long enough for first timeout and see if it fired.
   MessageLoop::current()->PostDelayedTask(FROM_HERE,
                                           new MessageLoop::QuitTask(), 40);
   MessageLoop::current()->Run();
   EXPECT_TRUE(host_->unresponsive_timer_fired());
 }