Made MixerAudioSource a pure interface.

webrtc/modules/audio_mixer/audio_mixer.gypi

Index: webrtc/modules/audio_mixer/audio_mixer.gypi
diff --git a/webrtc/modules/audio_mixer/audio_mixer.gypi b/webrtc/modules/audio_mixer/audio_mixer.gypi
index 43b25a40f6704e8a5c83ca4bf5fb6efb131663d6..6ea5145186f0b91d0b90de756194607382d9756e 100644
--- a/webrtc/modules/audio_mixer/audio_mixer.gypi
+++ b/webrtc/modules/audio_mixer/audio_mixer.gypi
@@ -15,6 +15,7 @@
         'audio_processing',
         'webrtc_utility',
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
+        '<(webrtc_root)/base/base.gyp:gtest_prod',

[the sun, 2016/10/06 09:50:31]

remove

[aleloi, 2016/10/06 12:17:12]

Done.

         '<(webrtc_root)/base/base.gyp:rtc_base_approved',
         '<(webrtc_root)/voice_engine/voice_engine.gyp:level_indicator',
       ],
@@ -22,10 +23,11 @@
         'audio_frame_manipulator.cc',
         'audio_frame_manipulator.h',
         'audio_mixer.h',
-        'audio_mixer_defines.cc',
         'audio_mixer_defines.h',
         'audio_mixer_impl.cc',
         'audio_mixer_impl.h',
+        'audio_source_with_mix_status.cc',
+        'audio_source_with_mix_status.h',
       ],
     },
   ], # targets