Fire visibilityChange event on out-of-process iframes.

content/common/page_messages.h

 // Copyright 2016 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/common/page_message_enums.h"
 #include "ipc/ipc_message_macros.h"
 #include "ui/gfx/geometry/rect.h"
 
 // IPC messages for page-level actions.
 // Multiply-included message file, hence no include guard.
 
 #undef IPC_MESSAGE_EXPORT
 #define IPC_MESSAGE_EXPORT CONTENT_EXPORT
 
 #define IPC_MESSAGE_START PageMsgStart
 
 IPC_ENUM_TRAITS_MAX_VALUE(
     PageMsg_SetZoomLevel_Command,
     PageMsg_SetZoomLevel_Command::LAST)
 
 // Messages sent from the browser to the renderer.
 
 IPC_MESSAGE_ROUTED1(PageMsg_UpdateWindowScreenRect,
                     gfx::Rect /* window_screen_rect */)
 
 IPC_MESSAGE_ROUTED2(PageMsg_SetZoomLevel,
                     PageMsg_SetZoomLevel_Command /* command */,
                     double /* zoom_level */)
 
+// Informs the renderer that the page was hidden.
+IPC_MESSAGE_ROUTED0(PageMsg_WasHidden)
+
+// Informs the renderer that the page is no longer hidden.
+IPC_MESSAGE_ROUTED0(PageMsg_WasShown)
+
 // -----------------------------------------------------------------------------
 // Messages sent from the renderer to the browser.
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent PageMsg, then ifdefs for platform specific PageMsg, then platform
 // independent PageHostMsg, then ifdefs for platform specific PageHostMsg.