Get rid of MessageLoop* caching in extensions code.

chrome/browser/extensions/pack_extension_job.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_EXTENSIONS_PACK_EXTENSION_JOB_UI_H_
 #define CHROME_BROWSER_EXTENSIONS_PACK_EXTENSION_JOB_UI_H_
 
 #include <string>
 
 #include "base/file_path.h"
 #include "base/ref_counted.h"
+#include "chrome/browser/chrome_thread.h"
 
-class MessageLoop;
 
 // Manages packing an extension on the file thread and reporting the result
 // back to the UI.
 class PackExtensionJob : public base::RefCountedThreadSafe<PackExtensionJob> {
  public:
 
   // Interface for people who want to use PackExtensionJob to implement.
   class Client {
    public:
     virtual void OnPackSuccess(const FilePath& crx_file,
                                const FilePath& key_file) = 0;
     virtual void OnPackFailure(const std::wstring& message) = 0;
   };
 
   PackExtensionJob(Client* client,
                    const FilePath& root_directory,
                    const FilePath& key_file);
 
   // The client should call this when it is destroyed to prevent
   // PackExtensionJob from attempting to access it.
   void ClearClient();
 
  private:
   void RunOnFileThread();
   void ReportSuccessOnUIThread();
   void ReportFailureOnUIThread(const std::string& error);
 
-  MessageLoop* ui_loop_;
+  ChromeThread::ID client_thread_id_;
   Client* client_;
   FilePath root_directory_;
   FilePath key_file_;
   FilePath crx_file_out_;
   FilePath key_file_out_;
 
   DISALLOW_COPY_AND_ASSIGN(PackExtensionJob);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_PACK_EXTENSION_JOB_UI_H_