[WebView] Add a new flushVisualState API to AwContents.

content/common/frame_messages.h

 // Copyright 2013 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 interacting with frames.
 // Multiply-included message file, hence no include guard.
 
 #include "content/common/content_export.h"
 #include "content/common/content_param_traits.h"
 #include "content/common/frame_message_enums.h"
@@ skipping 362 matching lines @@
                     content::CustomContextMenuContext /* custom_context */)
 
 // Executes custom context menu action that was provided from Blink.
 IPC_MESSAGE_ROUTED2(FrameMsg_CustomContextMenuAction,
                     content::CustomContextMenuContext /* custom_context */,
                     unsigned /* action */)
 
 // Requests that the RenderFrame or RenderFrameProxy sets its opener to null.
 IPC_MESSAGE_ROUTED0(FrameMsg_DisownOpener)
 
+// Requests that the RenderFrame send back a response synchronized with the

[Tom Sepez, 2015/01/08 18:15:27]

nit: not sure what "synchronized with the mechansim" means.  After the frame has
been delivered?  After all visual state has been flushed?

[Ignacio Solla, 2015/01/08 18:50:20]

Let me know if the comment is now clearer.

+// mechanism used to deliver new frames to the screen.
+IPC_MESSAGE_ROUTED1(FrameMsg_FlushVisualStateRequest,
+                    int /* id */)
+
 // Instructs the renderer to create a new RenderFrame object with |routing_id|.
 // The new frame should be created as a child of the object identified by
 // |parent_routing_id| or as top level if that is MSG_ROUTING_NONE.
 // If a valid |proxy_routing_id| is provided, the new frame will be configured
 // to replace the proxy on commit.
 IPC_MESSAGE_CONTROL3(FrameMsg_NewFrame,
                      int /* routing_id */,
                      int /* parent_routing_id */,
                      int /* proxy_routing_id */)
 
@@ skipping 430 matching lines @@
 // PlzNavigate
 // Tells the browser to perform a navigation.
 IPC_MESSAGE_ROUTED2(FrameHostMsg_BeginNavigation,
                     FrameHostMsg_BeginNavigation_Params,
                     content::CommonNavigationParams)
 
 // Sent once a paint happens after the first non empty layout. In other words
 // after the frame has painted something.
 IPC_MESSAGE_ROUTED0(FrameHostMsg_DidFirstVisuallyNonEmptyPaint)
 
+// Sent as a response to FrameMsg_FlushVisualStateRequest.
+// The message is delivered using RenderWidget::QueueMessage.
+IPC_MESSAGE_ROUTED1(FrameHostMsg_FlushVisualStateResponse,
+                    int /* id */)
+
 #if defined(OS_MACOSX) || defined(OS_ANDROID)
 
 // Message to show/hide a popup menu using native controls.
 IPC_MESSAGE_ROUTED1(FrameHostMsg_ShowPopup,
                     FrameHostMsg_ShowPopup_Params)
 IPC_MESSAGE_ROUTED0(FrameHostMsg_HidePopup)
 
 #endif