Move audio frame memory handling inside AudioMixer.

webrtc/api/audio/audio_mixer.h

Index: webrtc/api/audio/audio_mixer.h
diff --git a/webrtc/api/audio/audio_mixer.h b/webrtc/api/audio/audio_mixer.h
index eea79ae6535e316397b76da13c0bfb778a0767fa..895e18cc8ec931c37dca0ddfaa791389bd38629d 100644
--- a/webrtc/api/audio/audio_mixer.h
+++ b/webrtc/api/audio/audio_mixer.h
@@ -32,21 +32,15 @@ class AudioMixer : public rtc::RefCountInterface {
       kError,   // The audio_frame will not be used.
     };
 
-    struct AudioFrameWithInfo {
-      AudioFrame* audio_frame;
-      AudioFrameInfo audio_frame_info;
-    };
-
-    // The implementation of GetAudioFrameWithInfo should update
-    // audio_frame with new audio every time it's called. Implementing
-    // classes are allowed to return the same AudioFrame pointer on
-    // different calls. The pointer must stay valid until the next
-    // mixing call or until this audio source is disconnected from the
-    // mixer. The mixer may modify the contents of the passed
-    // AudioFrame pointer at any time until the next call to
-    // GetAudioFrameWithInfo, or until the source is removed from the
-    // mixer.
-    virtual AudioFrameWithInfo GetAudioFrameWithInfo(int sample_rate_hz) = 0;
+    // The AudioFrame pointer should be treated as only valid for the
+    // duration of this call. The passed AudioFrame is strictly an
+    // output parameter and its fields can have any values when being
+    // passed to GetAudioFrameWithInfo. Implementing classes may
+    // return sound with either one or two interleaved
+    // channels. Implementing classes are responsible for filling all
+    // fields of the provided AudioFrame with meaningful values.
+    virtual AudioFrameInfo GetAudioFrameWithInfo(int sample_rate_hz,
+                                                 AudioFrame* audio_frame) = 0;
 
     // A way for a mixer implementation to distinguish participants.
     virtual int Ssrc() = 0;