Defer CGLFlushDrawable until OSX-requested drawRect to avoid spinning when window is obscured.

content/browser/renderer_host/render_widget_host_impl.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_impl.h"
 
 #include <utility>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 597 matching lines @@
     repaint_start_time_ = TimeTicks::Now();
     repaint_ack_pending_ = true;
     Send(new ViewMsg_Repaint(routing_id_, view_size));
   }
 
   TimeDelta max_delay = TimeDelta::FromMilliseconds(kPaintMsgTimeoutMS);
   TimeTicks end_time = TimeTicks::Now() + max_delay;
   do {
     TRACE_EVENT0("renderer_host", "GetBackingStore::WaitForUpdate");
 
+#if defined(OS_MACOSX)
+    view_->AboutToWaitForBackingStoreMsg();
+#endif
+
     // When we have asked the RenderWidget to resize, and we are still waiting
     // on a response, block for a little while to see if we can't get a response
     // before returning the old (incorrectly sized) backing store.
     IPC::Message msg;
     if (process_->WaitForBackingStoreMsg(routing_id_, max_delay, &msg)) {
       OnMessageReceived(msg);
 
       // For auto-resized views, current_size_ determines the view_size and it
       // may have changed during the handling of an UpdateRect message.
       if (should_auto_resize_)
@@ skipping 1150 matching lines @@
   // indicate that no callback is in progress (i.e. without this line
   // DelayedAutoResized will not get called again).
   new_auto_size_.SetSize(0, 0);
   if (!should_auto_resize_)
     return;
 
   OnRenderAutoResized(new_size);
 }
 
 }  // namespace content