Take 2 at browser_sync::ExtensionsActivityMonitor....

chrome/browser/sync/util/extensions_activity_monitor.h

 // Copyright (c) 2009 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_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_
 #define CHROME_BROWSER_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_
 
 #include "base/lock.h"
 #include "base/message_loop.h"
 #include "base/ref_counted.h"
@@ skipping 24 matching lines @@
     std::string extension_id;
 
     // How many times the extension successfully invoked a write
     // operation through the bookmarks API since the last CommitMessage.
     uint32 bookmark_write_count;
   };
 
   typedef std::map<std::string, Record> Records;
 
   // Creates an ExtensionsActivityMonitor to monitor extensions activities on
-  // |ui_loop|.
-  explicit ExtensionsActivityMonitor(MessageLoop* ui_loop);
+  // ChromeThread::UI.
+  ExtensionsActivityMonitor();
   ~ExtensionsActivityMonitor();
 
   // Fills |buffer| with snapshot of current records in constant time by
   // swapping.  This is done mutually exclusively w.r.t methods of this class.
   void GetAndClearRecords(Records* buffer);
 
   // Add |records| piece-wise (by extension id) to the set of active records.
   // This is done mutually exclusively w.r.t the methods of this class.
   void PutRecords(const Records& records);
 
   // NotificationObserver implementation.  Called on |ui_loop_|.
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,
                        const NotificationDetails& details);
  private:
   Records records_;
   mutable Lock records_lock_;
 
-  // Kept for convenience.
-  MessageLoop* const ui_loop_;
-
   // Used only from UI loop.
   NotificationRegistrar registrar_;
 };
 
 }  // namespace browser_sync
 
-#endif  // CHROME_BROWSER_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_
+#endif  // CHROME_BROWSER_SYNC_UTIL_EXTENSIONS_ACTIVITY_MONITOR_H_