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

content/common/view_messages.h

 // 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.
 
 // IPC messages for page rendering.
 // Multiply-included message file, hence no include guard.
 
 #include "base/process.h"
 #include "base/shared_memory.h"
 #include "content/common/content_export.h"
@@ skipping 1402 matching lines @@
 // the tag sent along with ViewMsg_PaintAtSize.
 IPC_MESSAGE_ROUTED2(ViewHostMsg_PaintAtSize_ACK,
                     int /* tag */,
                     gfx::Size /* size */)
 
 // Sent to update part of the view.  In response to this message, the host
 // generates a ViewMsg_UpdateRect_ACK message.
 IPC_MESSAGE_ROUTED1(ViewHostMsg_UpdateRect,
                     ViewHostMsg_UpdateRect_Params)
 
+// Sent to unblock the browser's UI thread if it is waiting on an UpdateRect,
+// which may get delayed until the browser's UI unblocks.
+IPC_MESSAGE_ROUTED0(ViewHostMsg_UpdateIsDelayed)
+
 // Sent by the renderer when accelerated compositing is enabled or disabled to
 // notify the browser whether or not is should do painting.
 IPC_MESSAGE_ROUTED1(ViewHostMsg_DidActivateAcceleratedCompositing,
                     bool /* true if the accelerated compositor is actve */)
 
 // Acknowledges receipt of a ViewMsg_HandleInputEvent message.
 IPC_MESSAGE_ROUTED2(ViewHostMsg_HandleInputEvent_ACK,
                     WebKit::WebInputEvent::Type,
                     bool /* processed */)
 
@@ skipping 510 matching lines @@
                      media::MediaLogEvent /* event */)
 
 // Requests to lock the mouse. Will result in a ViewMsg_LockMouse_ACK message
 // being sent back.
 IPC_MESSAGE_ROUTED0(ViewHostMsg_LockMouse)
 
 // Requests to unlock the mouse. A ViewMsg_MouseLockLost message will be sent
 // whenever the mouse is unlocked (which may or may not be caused by
 // ViewHostMsg_UnlockMouse).
 IPC_MESSAGE_ROUTED0(ViewHostMsg_UnlockMouse)