Convert channel counts to size_t.

webrtc/modules/audio_conference_mixer/source/audio_conference_mixer_impl.cc

Index: webrtc/modules/audio_conference_mixer/source/audio_conference_mixer_impl.cc
diff --git a/webrtc/modules/audio_conference_mixer/source/audio_conference_mixer_impl.cc b/webrtc/modules/audio_conference_mixer/source/audio_conference_mixer_impl.cc
index 0ac9eae691973322265e53ac9a297b5f1e779985..afb060f46df246d47685e3425692e6a94fc7c35a 100644
--- a/webrtc/modules/audio_conference_mixer/source/audio_conference_mixer_impl.cc
+++ b/webrtc/modules/audio_conference_mixer/source/audio_conference_mixer_impl.cc
@@ -50,8 +50,8 @@ void MixFrames(AudioFrame* mixed_frame, AudioFrame* frame, bool use_limiter) {
 }
 
 // Return the max number of channels from a |list| composed of AudioFrames.
-int MaxNumChannels(const AudioFrameList* list) {
-  int max_num_channels = 1;
+size_t MaxNumChannels(const AudioFrameList* list) {
+  size_t max_num_channels = 1;
   for (AudioFrameList::const_iterator iter = list->begin();
        iter != list->end();
        ++iter) {
@@ -278,7 +278,7 @@ int32_t AudioConferenceMixerImpl::Process() {
         //                with an API instead of dynamically.
 
         // Find the max channels over all mixing lists.
-        const int num_mixed_channels = std::max(MaxNumChannels(&mixList),
+        const size_t num_mixed_channels = std::max(MaxNumChannels(&mixList),
             std::max(MaxNumChannels(&additionalFramesList),
                      MaxNumChannels(&rampOutList)));