Add UMA histograms to MHTML save operations.

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 <stddef.h>
 #include <stdint.h>
 
@@ skipping 1478 matching lines @@
 // non-savable content (i.e. from a non-savable scheme) or if there were
 // errors gathering the links.
 IPC_MESSAGE_ROUTED0(FrameHostMsg_SavableResourceLinksError)
 
 // Response to FrameMsg_GetSerializedHtmlWithLocalLinks.
 IPC_MESSAGE_ROUTED2(FrameHostMsg_SerializedHtmlWithLocalLinksResponse,
                     std::string /* data buffer */,
                     bool /* end of data? */)
 
 // Response to FrameMsg_SerializeAsMHTML.
-IPC_MESSAGE_ROUTED3(
+IPC_MESSAGE_ROUTED4(
     FrameHostMsg_SerializeAsMHTMLResponse,
     int /* job_id (used to match responses to requests) */,
     bool /* true if success, false if error */,
-    std::set<std::string> /* digests of uris of serialized resources */)
+    std::set<std::string> /* digests of uris of serialized resources */,
+    base::TimeDelta /* how much time of the main render thread was used */)
 
 // Sent when the renderer updates hint for importance of a tab.
 IPC_MESSAGE_ROUTED1(FrameHostMsg_UpdatePageImportanceSignals,
                     content::PageImportanceSignals)
 
 // This message is sent from a RenderFrameProxy when sequential focus
 // navigation needs to advance into its actual frame.  |source_routing_id|
 // identifies the frame that issued this request.  This is used when pressing
 // <tab> or <shift-tab> hits an out-of-process iframe when searching for the
 // next focusable element.
@@ skipping 55 matching lines @@
 // nearest find result in the sending frame.
 IPC_MESSAGE_ROUTED2(FrameHostMsg_GetNearestFindResult_Reply,
                     int /* nfr_request_id */,
                     float /* distance */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent FrameMsg, then ifdefs for platform specific FrameMsg, then
 // platform independent FrameHostMsg, then ifdefs for platform specific
 // FrameHostMsg.