Delete the temporary file when generating MHTML with the extension API.

chrome/common/extensions/extension_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 extensions.
 // Multiply-included message file, hence no include guard.
 
 #include "base/shared_memory.h"
 #include "base/values.h"
 #include "chrome/common/extensions/extension.h"
@@ skipping 338 matching lines @@
                     std::string /* error */)
 
 // Sent by the renderer when an App is requesting permission to send server
 // pushed notifications.
 IPC_MESSAGE_ROUTED4(ExtensionHostMsg_GetAppNotifyChannel,
                     GURL /* requestor_url */,
                     std::string /* client_id */,
                     int32 /* return_route_id */,
                     int32 /* callback_id */)
 
+// Optional Ack message sent to the browser to notify that the response to a
+// function has been processed.
+IPC_MESSAGE_ROUTED1(ExtensionHostMsg_ResponseAck,
+                    int /* request_id */)
+
 // Response to the renderer for the above message.
 IPC_MESSAGE_ROUTED3(ExtensionMsg_GetAppNotifyChannelResponse,
                     std::string /* channel_id */,
                     std::string /* error */,
                     int32 /* callback_id */)
 
 // Deliver a message sent with ExtensionHostMsg_PostMessage.
 IPC_MESSAGE_ROUTED2(ExtensionMsg_DeliverMessage,
                     int /* target_port_id */,
                     std::string /* message */)