Add MuteableAudioOutputStream interface to export SetMute().

media/audio/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/linux/pkg_config.gni")
 import("//media/media_options.gni")
 
 # When libpulse is not directly linked, use stubs to allow for dlopening of the
 # binary.
 if (!link_pulseaudio) {
@@ skipping 190 matching lines @@
       "winmm.lib",
     ]
   }
 
   if (is_android) {
     sources += [
       "android/audio_manager_android.cc",
       "android/audio_manager_android.h",
       "android/audio_record_input.cc",
       "android/audio_record_input.h",
+      "android/muteable_audio_output_stream.h",
       "android/opensles_input.cc",
       "android/opensles_input.h",
       "android/opensles_output.cc",
       "android/opensles_output.h",
       "android/opensles_util.cc",
       "android/opensles_util.h",
       "android/opensles_wrapper.cc",
     ]
     deps += [ "//media/base/android:media_jni_headers" ]
   }
@@ skipping 177 matching lines @@
     ]
   }
 
   if (use_alsa) {
     sources += [
       "alsa/alsa_output_unittest.cc",
       "audio_low_latency_input_output_unittest.cc",
     ]
   }
 }