Adds tracing to MHTML generation call chain.

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 59 matching lines @@
   // been created.
   void OnFileAvailable(int job_id, base::File browser_file);
 
   // Called on the UI thread when a job has been finished.
   void JobFinished(Job* job, JobStatus job_status);
 
   // Called on the UI thread after the file got finalized and we have its size.
   void OnFileClosed(int job_id, JobStatus job_status, int64_t file_size);
 
   // Creates and registers a new job.
-  int NewJob(WebContents* web_contents,
-             const MHTMLGenerationParams& params,
-             const GenerateMHTMLCallback& callback);
+  Job* NewJob(WebContents* web_contents,
+              const MHTMLGenerationParams& params,
+              const GenerateMHTMLCallback& callback);
 
   // Finds job by id.  Returns nullptr if no job with a given id was found.
   Job* FindJob(int job_id);
 
   // Called when the render process connected to a job exits.
   void RenderProcessExited(Job* job);
 
   typedef std::map<int, Job*> IDToJobMap;
   IDToJobMap id_to_job_;
 
   int next_job_id_;
 
   DISALLOW_COPY_AND_ASSIGN(MHTMLGenerationManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_MHTML_GENERATION_MANAGER_H_