Added a kEchoCancellation constraint to turn off the audio processing.

content/content_tests.gypi

 # Copyright (c) 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.
 
 {
   'targets': [
     {
       'target_name': 'layouttest_support_content',
       'type': 'static_library',
       'conditions': [
@@ skipping 727 matching lines @@
           'sources': [
             'browser/media/webrtc_internals_unittest.cc',
             'browser/renderer_host/media/webrtc_identity_service_host_unittest.cc',
             'browser/renderer_host/p2p/socket_host_test_utils.cc',
             'browser/renderer_host/p2p/socket_host_test_utils.h',
             'browser/renderer_host/p2p/socket_host_tcp_unittest.cc',
             'browser/renderer_host/p2p/socket_host_tcp_server_unittest.cc',
             'browser/renderer_host/p2p/socket_host_udp_unittest.cc',
             'browser/renderer_host/p2p/socket_host_unittest.cc',
             'renderer/media/media_stream_audio_processor_unittest.cc',
+            'renderer/media/media_stream_constraints_util_unittest.cc',
             'renderer/media/media_stream_dependency_factory_unittest.cc',
             'renderer/media/media_stream_dispatcher_unittest.cc',
             'renderer/media/media_stream_impl_unittest.cc',
             'renderer/media/media_stream_video_capture_source_unittest.cc',
             'renderer/media/media_stream_video_source_unittest.cc',
             'renderer/media/media_stream_video_track_unittest.cc',
             'renderer/media/mock_media_stream_registry.cc',
             'renderer/media/mock_media_stream_registry.h',
             'renderer/media/mock_media_stream_video_sink.cc',
             'renderer/media/mock_media_stream_video_sink.h',
@@ skipping 1061 matching lines @@
                   'files': ['<(PRODUCT_DIR)/libnpapi_test_plugin.so'],
                 },
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }