Add support for 'start_url' in Manifest.

content/common/manifest_manager_messages.h

 // Copyright 2014 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 the web manifest manager.
 // Multiply-included message file, hence no include guard.
 
 #include "content/common/content_export.h"
 #include "content/public/common/manifest.h"
 #include "ipc/ipc_message_macros.h"
 
 #undef IPC_MESSAGE_EXPORT
 #define IPC_MESSAGE_EXPORT CONTENT_EXPORT
 
 #define IPC_MESSAGE_START ManifestManagerMsgStart
 
 IPC_STRUCT_TRAITS_BEGIN(content::Manifest)
   IPC_STRUCT_TRAITS_MEMBER(name)
   IPC_STRUCT_TRAITS_MEMBER(short_name)
+  IPC_STRUCT_TRAITS_MEMBER(start_url)
 IPC_STRUCT_TRAITS_END()
 
 // The browser process requests for the manifest linked with the associated
 // render frame. The renderer process will respond via a RequestManifestResponse
 // IPC message with a Manifest object attached to it and the associated
 // |request_id| that was initially given.
 IPC_MESSAGE_ROUTED1(ManifestManagerMsg_RequestManifest,
                     int /* request_id */)
 
 // The renderer process' response to a RequestManifest. The |request_id| will
 // match the one that was initially received. The |manifest| object will be an
 // empty manifest in case of any failure.
 IPC_MESSAGE_ROUTED2(ManifestManagerHostMsg_RequestManifestResponse,
                     int, /* request_id */
                     content::Manifest /* manifest */)