Add metrics regarding concurrent audible tabs in Chromium.

content/content_browser.gypi

 # Copyright (c) 2012 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.
 
 {
   'dependencies': [
     '../base/base.gyp:base_static',
     '../components/url_formatter/url_formatter.gyp:url_formatter',
     '../crypto/crypto.gyp:crypto',
     '../device/battery/battery.gyp:device_battery',
@@ skipping 984 matching lines @@
       'browser/media/android/media_session_uma_helper.cc',
       'browser/media/android/media_session_uma_helper.h',
       'browser/media/android/media_throttler.cc',
       'browser/media/android/media_throttler.h',
       'browser/media/android/media_web_contents_observer_android.cc',
       'browser/media/android/media_web_contents_observer_android.h',
       'browser/media/android/provision_fetcher_impl.cc',
       'browser/media/android/provision_fetcher_impl.h',
       'browser/media/android/url_provision_fetcher.cc',
       'browser/media/android/url_provision_fetcher.h',
+      'browser/media/audible_metrics.cc',
+      'browser/media/audible_metrics.h',
       'browser/media/audio_stream_monitor.cc',
       'browser/media/audio_stream_monitor.h',
       'browser/media/capture/audio_mirroring_manager.cc',
       'browser/media/capture/audio_mirroring_manager.h',
       'browser/media/capture/cursor_renderer.h',
       'browser/media/capture/cursor_renderer_aura.cc',
       'browser/media/capture/cursor_renderer_aura.h',
       'browser/media/capture/web_contents_audio_input_stream.cc',
       'browser/media/capture/web_contents_audio_input_stream.h',
       'browser/media/capture/web_contents_audio_muter.cc',
@@ skipping 1196 matching lines @@
     ['enable_webvr==1 and OS=="android"', {
       'sources': [
         'browser/vr/android/cardboard/cardboard_vr_device.cc',
         'browser/vr/android/cardboard/cardboard_vr_device.h',
         'browser/vr/android/cardboard/cardboard_vr_device_provider.cc',
         'browser/vr/android/cardboard/cardboard_vr_device_provider.h',
       ],
     }],
   ],
 }