Convert WebRtcLoggingHandlerHost to use the blocking thread pool.

chrome/browser/media/webrtc_log_util.h

Index: chrome/browser/media/webrtc_log_util.h
===================================================================
--- chrome/browser/media/webrtc_log_util.h	(revision 273292)
+++ chrome/browser/media/webrtc_log_util.h	(working copy)
@@ -5,19 +5,22 @@
 #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);