Added A/V sync tests with drifting clocks.

webrtc/test/webrtc_test_common.gyp

 # Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 {
   'includes': [
     '../build/common.gypi',
   ],
   'targets': [
     {
       'target_name': 'webrtc_test_common',
       'type': 'static_library',
       'sources': [
         'call_test.cc',
         'call_test.h',
         'configurable_frame_size_encoder.cc',
         'configurable_frame_size_encoder.h',
         'constants.cc',
         'constants.h',
         'direct_transport.cc',
         'direct_transport.h',
+        'drifting_clock.cc',
+        'drifting_clock.h',
         'encoder_settings.cc',
         'encoder_settings.h',
         'fake_audio_device.cc',
         'fake_audio_device.h',
         'fake_decoder.cc',
         'fake_decoder.h',
         'fake_encoder.cc',
         'fake_encoder.h',
         'fake_network_pipe.cc',
         'fake_network_pipe.h',
@@ skipping 144 matching lines @@
             'fake_network_pipe_unittest.cc',
             'frame_generator_unittest.cc',
             'rtp_file_reader_unittest.cc',
             'rtp_file_writer_unittest.cc',
           ],
         },
       ],  #targets
     }],  # include_tests
   ],  # conditions
 }