Delete background tab IOSurfaces on Mac.

content/renderer/render_widget.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/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 1063 matching lines @@
       FROM_HERE, base::Bind(&RenderWidget::InvalidationCallback, this));
 }
 
 void RenderWidget::didAutoResize(const WebSize& new_size) {
   size_ = new_size;
 }
 
 void RenderWidget::didActivateCompositor(int input_handler_identifier) {
   TRACE_EVENT0("gpu", "RenderWidget::didActivateCompositor");
 
+#if !defined(OS_MACOSX)
   if (!is_accelerated_compositing_active_) {
     // When not in accelerated compositing mode, in certain cases (e.g. waiting
     // for a resize or if no backing store) the RenderWidgetHost is blocking the
     // browser's UI thread for some time, waiting for an UpdateRect. If we are
     // going to switch to accelerated compositing, the GPU process may need
     // round-trips to the browser's UI thread before finishing the frame,
     // causing deadlocks if we delay the UpdateRect until we receive the
     // OnSwapBuffersComplete.  So send a dummy message that will unblock the
-    // browser's UI thread.
+    // browser's UI thread. This is not necessary on Mac, because SwapBuffers
+    // now unblocks GetBackingStore on Mac.
     Send(new ViewHostMsg_UpdateIsDelayed(routing_id_));
   }
+#endif
 
   is_accelerated_compositing_active_ = true;
   Send(new ViewHostMsg_DidActivateAcceleratedCompositing(
       routing_id_, is_accelerated_compositing_active_));
 }
 
 void RenderWidget::didDeactivateCompositor() {
   TRACE_EVENT0("gpu", "RenderWidget::didDeactivateCompositor");
 
   is_accelerated_compositing_active_ = false;
@@ skipping 588 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }