Moved MixerAudioSource and removed audio_mixer_defines.h.

webrtc/modules/audio_mixer/audio_frame_manipulator.cc

Index: webrtc/modules/audio_mixer/audio_frame_manipulator.cc
diff --git a/webrtc/modules/audio_mixer/audio_frame_manipulator.cc b/webrtc/modules/audio_mixer/audio_frame_manipulator.cc
index 7ced9e29fa9e1c522c0c2de0cb3a1a9e990ec386..b8274d3f62d0443165492a5bd1afd7b0fda2b142 100644
--- a/webrtc/modules/audio_mixer/audio_frame_manipulator.cc
+++ b/webrtc/modules/audio_mixer/audio_frame_manipulator.cc
@@ -8,8 +8,10 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#include "webrtc/base/checks.h"
 #include "webrtc/modules/audio_mixer/audio_frame_manipulator.h"
 #include "webrtc/modules/include/module_common_types.h"
+#include "webrtc/modules/utility/include/audio_frame_operations.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
@@ -59,4 +61,15 @@ void NewMixerRampOut(AudioFrame* audio_frame) {
          (audio_frame->samples_per_channel_ - kRampSize) *
              sizeof(audio_frame->data_[0]));
 }
+
+void RemixFrame(AudioFrame* frame, size_t target_number_of_channels) {

[hlundin-webrtc, 2016/10/11 11:11:49]

Put input parameters before input/output parameters.
https://google.github.io/styleguide/cppguide.html#Function_Parameter_Ordering

[aleloi, 2016/10/11 11:48:57]

Thanks for noticing! I did the same mistake in the next commit for Ramp.

+  RTC_DCHECK_GE(target_number_of_channels, static_cast<size_t>(1));

[hlundin-webrtc, 2016/10/11 11:11:49]

Can't you write 1u and 2u instead of static_cast...?

[aleloi, 2016/10/11 11:48:57]

I've already changed this in the next dependent CL (solenberg@ pointed out the
same issue in another place).

[hlundin-webrtc, 2016/10/11 11:54:11]

Acknowledged.

+  RTC_DCHECK_LE(target_number_of_channels, static_cast<size_t>(2));
+  if (frame->num_channels_ == 1 && target_number_of_channels == 2) {
+    AudioFrameOperations::MonoToStereo(frame);
+  } else if (frame->num_channels_ == 2 && target_number_of_channels == 1) {
+    AudioFrameOperations::StereoToMono(frame);
+  }
+}
+
 }  // namespace webrtc