Get rid of MessageLoop* caching in extensions code.

chrome/browser/chrome_thread.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_CHROME_THREAD_H_
 #define CHROME_BROWSER_CHROME_THREAD_H_
 
 #include "base/lock.h"
 #include "base/task.h"
 #include "base/thread.h"
@@ skipping 103 matching lines @@
   // Callable on any thread.  Returns whether you're currently on a particular
   // thread.
   //
   // WARNING:
   //   When running under unit-tests, this will return true if you're on the
   //   main thread and the thread ID you pass in isn't running.  This is
   //   normally the correct behavior because you want to ignore these asserts
   //   unless you've specifically spun up the threads, but be mindful of it.
   static bool CurrentlyOn(ID identifier);
 
+  // If the current message loop is one of the known threads, returns true and
+  // sets identifier to its ID.  Otherwise returns false.
+  static bool GetCurrentThreadIdentifier(ID* identifier);
+
  private:
   // Common initialization code for the constructors.
   void Initialize();
 
-  // If the current message loop is one of the known threads, returns true and
-  // sets identifier to its ID.  Otherwise returns false.
-  static bool GetCurrentThreadIdentifier(ID* identifier);
-
   static bool PostTaskHelper(
       ID identifier,
       const tracked_objects::Location& from_here,
       Task* task,
       int64 delay_ms,
       bool nestable);
 
   // The identifier of this thread.  Only one thread can exist with a given
   // identifier at a given time.
   ID identifier_;
 
   // This lock protects |chrome_threads_|.  Do not read or modify that array
   // without holding this lock.  Do not block while holding this lock.
   static Lock lock_;
 
   // An array of the ChromeThread objects.  This array is protected by |lock_|.
   // The threads are not owned by this array.  Typically, the threads are owned
   // on the UI thread by the g_browser_process object.  ChromeThreads remove
   // themselves from this array upon destruction.
   static ChromeThread* chrome_threads_[ID_COUNT];
 };
 
 #endif  // #ifndef CHROME_BROWSER_CHROME_THREAD_H_