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

chrome/browser/sync/glue/ui_model_worker_unittest.cc

 // 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.
 
 #include "base/callback.h"
 #include "base/message_loop.h"
 #include "base/ref_counted.h"
 #include "base/thread.h"
+#include "base/waitable_event.h"
 #include "chrome/browser/sync/engine/syncapi.h"
 #include "chrome/browser/sync/glue/ui_model_worker.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using browser_sync::UIModelWorker;
 using namespace sync_api;
 
 // Various boilerplate, primarily for the StopWithPendingWork test.
 
 class UIModelWorkerVisitor {
@@ skipping 198 matching lines @@
       new FakeSyncShareTask(syncer(), fox3.get()));
 
   // This is what gets the UI thread blocked until NotifyExitRequested,
   // which is called when FakeSyncapiShutdownTask runs and deletes the syncer.
   bmw()->Stop();
 
   // Was the thread killed?
   EXPECT_FALSE(syncer_thread()->IsRunning());
   core_thread()->Stop();
 }