Update audio code to use size_t more correctly, webrtc/voice_engine/ portion.

webrtc/voice_engine/transmit_mixer_unittest.cc

Index: webrtc/voice_engine/transmit_mixer_unittest.cc
diff --git a/webrtc/voice_engine/transmit_mixer_unittest.cc b/webrtc/voice_engine/transmit_mixer_unittest.cc
index 5fb982b1fc33c503f284528fa7f731b0b099b75c..27aa8b3f014ac5a9f7d0fbcd70929592ca5f4097 100644
--- a/webrtc/voice_engine/transmit_mixer_unittest.cc
+++ b/webrtc/voice_engine/transmit_mixer_unittest.cc
@@ -20,7 +20,7 @@ namespace {
 class MediaCallback : public VoEMediaProcess {
  public:
   virtual void Process(int channel, ProcessingTypes type,
-                       int16_t audio[], int samples_per_channel,
+                       int16_t audio[], size_t samples_per_channel,
                        int sample_rate_hz, bool is_stereo) {
   }
 };