FBTF: Remove unneeded headers from base/ (part 2)

chrome/browser/sync/glue/ui_model_worker.h

 // Copyright (c) 2010 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_GLUE_UI_MODEL_WORKER_H_
 #define CHROME_BROWSER_SYNC_GLUE_UI_MODEL_WORKER_H_
 #pragma once
 
 #include "base/callback.h"
 #include "base/condition_variable.h"
 #include "base/lock.h"
 #include "base/task.h"
-#include "base/waitable_event.h"
 #include "chrome/browser/sync/engine/syncapi.h"
 #include "chrome/browser/sync/engine/model_safe_worker.h"
 
+namespace base {
+class WaitableEvent;
+}
+
 class MessageLoop;
 
 namespace browser_sync {
 
 // A ModelSafeWorker for UI models (e.g. bookmarks) that accepts work requests
 // from the syncapi that need to be fulfilled from the MessageLoop home to the
 // native model.
 //
 // Lifetime note: Instances of this class will generally be owned by the
 // SyncerThread. When the SyncerThread _object_ is destroyed, the
@@ skipping 103 matching lines @@
   // SyncerThread has terminated. We only care about (1) when we are in Stop(),
   // because we have to manually Run() the task.
   ConditionVariable syncapi_event_;
 
   DISALLOW_COPY_AND_ASSIGN(UIModelWorker);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_UI_MODEL_WORKER_H_