[WebView] Add a new flushVisualState API to AwContents.

content/common/frame_messages.h

Index: content/common/frame_messages.h
diff --git a/content/common/frame_messages.h b/content/common/frame_messages.h
index 31fa6039d956dcf194fc077a6440a4dd1cce9896..94e361db8a90a6eb47ee285f89d4a444c341c679 100644
--- a/content/common/frame_messages.h
+++ b/content/common/frame_messages.h
@@ -380,6 +380,11 @@ IPC_MESSAGE_ROUTED2(FrameMsg_CustomContextMenuAction,
 // Requests that the RenderFrame or RenderFrameProxy sets its opener to null.
 IPC_MESSAGE_ROUTED0(FrameMsg_DisownOpener)
 
+// Requests that the RenderFrame send back a response after waiting for the
+// commit, activation and frame swap of the current DOM tree in blink.
+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.
@@ -830,6 +835,11 @@ IPC_MESSAGE_ROUTED2(FrameHostMsg_BeginNavigation,
 // 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.