Move audio frame memory handling inside AudioMixer.

webrtc/modules/audio_mixer/audio_mixer_impl.h

Index: webrtc/modules/audio_mixer/audio_mixer_impl.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.h b/webrtc/modules/audio_mixer/audio_mixer_impl.h
index 500bb7862e5defe2b9fd906c057c6cf60fec3087..fdc097653094fe64c8e81c3a4780df8fe6548d85 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.h
@@ -35,9 +35,12 @@ class AudioMixerImpl : public AudioMixer {
     Source* audio_source = nullptr;
     bool is_mixed = false;
     float gain = 0.0f;
+
+    // A frame that will be passed to audio_source->GetAudioFrameWithInfo.
+    AudioFrame audio_frame{};

[the sun, 2016/10/18 14:06:17]

Do you really need the {} ?
Also, I thought this type of initialization was not permitted according to the
style guide, but I may be mixing things up.

[aleloi, 2016/10/18 14:17:48]

It's a (brace) default member initializer
(http://en.cppreference.com/w/cpp/language/data_members#Member_initialization).
It makes the audio frame to be initialized with its default constructor. I am
not sure, but I think the frame will not get initialized otherwise. That was how
I understood the documentation section from the link above.

I think the style guide is OK with this
(https://engdoc.corp.google.com/eng/doc/devguide/cpp/styleguide.shtml?cl=head#...)

[the sun, 2016/10/18 14:21:45]

The default ctor will be called without the {}.

[aleloi, 2016/10/18 14:30:41]

Right, because it is a class and then the default constructor is run unless
there is a default member initializer or if the member is present in an
initialization list. Fixed.

   };
 
-  typedef std::vector<SourceStatus> SourceStatusList;
+  using SourceStatusList = std::vector<std::unique_ptr<SourceStatus>>;
 
   // AudioProcessing only accepts 10 ms frames.
   static const int kFrameDurationInMs = 10;