Add UMA histograms to MHTML save operations.

content/browser/download/mhtml_generation_manager.h

 // Copyright (c) 2012 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.
 #ifndef CONTENT_BROWSER_DOWNLOAD_MHTML_GENERATION_MANAGER_H_
 #define CONTENT_BROWSER_DOWNLOAD_MHTML_GENERATION_MANAGER_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <set>
@@ skipping 35 matching lines @@
   void SaveMHTML(WebContents* web_contents,
                  const MHTMLGenerationParams& params,
                  const GenerateMHTMLCallback& callback);
 
   // Handler for FrameHostMsg_SerializeAsMHTMLResponse (a notification from the
   // renderer that the MHTML generation finished for a single frame).
   void OnSerializeAsMHTMLResponse(
       RenderFrameHostImpl* sender,
       int job_id,
       bool mhtml_generation_in_renderer_succeeded,
-      const std::set<std::string>& digests_of_uris_of_serialized_resources);
+      const std::set<std::string>& digests_of_uris_of_serialized_resources,
+      base::TimeDelta renderer_main_thread_time);
 
  private:
   friend struct base::DefaultSingletonTraits<MHTMLGenerationManager>;
   class Job;
   enum class JobStatus { SUCCESS, FAILURE };
 
   MHTMLGenerationManager();
   virtual ~MHTMLGenerationManager();
 
   // Called on the file thread to create |file|.
@@ skipping 24 matching lines @@
   IDToJobMap id_to_job_;
 
   int next_job_id_;
 
   DISALLOW_COPY_AND_ASSIGN(MHTMLGenerationManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_MHTML_GENERATION_MANAGER_H_