Remove unneeded platform_thread.h includes. Reduces number of includes from 5...

media/base/pipeline_impl_unittest.cc

 // Copyright (c) 2006-2009 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.
 
 #include <string>
 
-#include "base/platform_thread.h"
 #include "base/time.h"
 #include "base/waitable_event.h"
 #include "media/base/pipeline_impl.h"
 #include "media/base/media_format.h"
 #include "media/base/filters.h"
 #include "media/base/factory.h"
 #include "media/base/filter_host.h"
 #include "media/base/mock_media_filters.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 127 matching lines @@
   config.has_video = false;
   AddAllMockFilters(c, &config);
   InitializationHelper h;
   h.Start(&p, c, url, media::PIPELINE_ERROR_COULD_NOT_RENDER);
   p.Stop();
 }
 
 // TODO(ralphl): Add a unit test that makes sure that the mock audio filter
 // is actually called on a SetVolume() call to the pipeline.  I almost checked
 // in code that broke this, but all unit tests were passing.