Convert WebRtcLoggingHandlerHost to use the blocking thread pool.

chrome/browser/media/webrtc_log_util.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.
 
 #ifndef CHROME_BROWSER_MEDIA_WEBRTC_LOG_UTIL_H_
 #define CHROME_BROWSER_MEDIA_WEBRTC_LOG_UTIL_H_
 
-#include "base/files/file_path.h"
-#include "base/time/time.h"
+namespace base {
+class FilePath;
+class Time;
+}
 
 class WebRtcLogUtil {
  public:
   // Deletes logs files older that 5 days. Updates the log file list. Must be
-  // called on the FILE thread.
+  // called on a thread that allows IO.
   static void DeleteOldWebRtcLogFiles(const base::FilePath& log_dir);
 
   // Deletes logs files older that 5 days and logs younger than
   // |delete_begin_time|. Updates the log file list. If |delete_begin_time| is
   // base::time::Max(), no recent logs will be deleted, and the function is
-  // equal to DeleteOldWebRtcLogFiles(). Must be called on the FILE thread.
+  // equal to DeleteOldWebRtcLogFiles(). Must be called on a thread that allows
+  // IO.
   static void DeleteOldAndRecentWebRtcLogFiles(
       const base::FilePath& log_dir,
       const base::Time& delete_begin_time);
 
   // Calls DeleteOldWebRtcLogFiles() for all profiles. Must be called on the UI
   // thread.
   static void DeleteOldWebRtcLogFilesForAllProfiles();
 };
 
 #endif  // CHROME_BROWSER_MEDIA_WEBRTC_LOG_UTIL_H_