Cleanup: Remove unneeded forward declarations from various chrome/browser subdirectories.

chrome/browser/metrics/field_trial_synchronizer.h

 // Copyright (c) 2011 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_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_
 #define CHROME_BROWSER_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_
 #pragma once
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/metrics/field_trial.h"
 
-class MessageLoop;
-class Task;
-
 // This class is used by the browser process to communicate FieldTrial setting
 // (field trial name and group) to any previously started renderers.
 //
 // This class registers itself as an observer of FieldTrialList. FieldTrialList
 // notifies this class by calling it's OnFieldTrialGroupFinalized method when a
 // group is selected (finalized) for a FieldTrial and OnFieldTrialGroupFinalized
 // method sends the FieldTrial's name and the group to all renderer processes.
 // Each renderer process creates the FieldTrial, and by using a 100% probability
 // for the FieldTrial, forces the FieldTrial to have the same group string.
 
@@ skipping 29 matching lines @@
   // This singleton instance should be constructed during the single threaded
   // portion of main(). It initializes globals to provide support for all future
   // calls. This object is created on the UI thread, and it is destroyed after
   // all the other threads have gone away.
   static FieldTrialSynchronizer* field_trial_synchronizer_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialSynchronizer);
 };
 
 #endif  // CHROME_BROWSER_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_