Fix mipsel compile error due to missing header.

content/common/gpu/media/video_encode_accelerator_unittest.cc

 // Copyright 2013 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 <inttypes.h>
 
 #include <algorithm>
 
 #include "base/at_exit.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/files/memory_mapped_file.h"
 #include "base/memory/scoped_vector.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/process/process_handle.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
 #include "base/sys_byteorder.h"
+#include "base/threading/thread.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "content/common/gpu/media/video_accelerator_unittest_helpers.h"
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/bitstream_buffer.h"
 #include "media/base/test_data_util.h"
 #include "media/filters/h264_parser.h"
 #include "media/video/fake_video_encode_accelerator.h"
 #include "media/video/video_encode_accelerator.h"
@@ skipping 1492 matching lines @@
 
   content::g_env =
       reinterpret_cast<content::VideoEncodeAcceleratorTestEnvironment*>(
           testing::AddGlobalTestEnvironment(
               new content::VideoEncodeAcceleratorTestEnvironment(
                   test_stream_data.Pass(), log_path, run_at_fps,
                   needs_encode_latency)));
 
   return RUN_ALL_TESTS();
 }