[NOT FOR REVIEW] Convert channel counts to size_t.

webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc

Index: webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
diff --git a/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc b/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
index 5e5c04b5e350064e8747c531c09488ec5d1c77a5..09ef8325096c431e37afa8faebef9941573bfd2d 100644
--- a/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
+++ b/webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc
@@ -1014,7 +1014,7 @@ bool AudioCodingImpl::RegisterSendCodec(int encoder_type,
                                         int frame_size_samples) {
   std::string codec_name;
   int sample_rate_hz;
-  int channels;
+  size_t channels;
   if (!MapCodecTypeToParameters(
           encoder_type, &codec_name, &sample_rate_hz, &channels)) {
     return false;
@@ -1063,7 +1063,7 @@ bool AudioCodingImpl::RegisterReceiveCodec(int decoder_type,
                                            uint8_t payload_type) {
   std::string codec_name;
   int sample_rate_hz;
-  int channels;
+  size_t channels;
   if (!MapCodecTypeToParameters(
           decoder_type, &codec_name, &sample_rate_hz, &channels)) {
     return false;
@@ -1150,7 +1150,7 @@ void AudioCodingImpl::GetDecodingCallStatistics(
 bool AudioCodingImpl::MapCodecTypeToParameters(int codec_type,
                                                std::string* codec_name,
                                                int* sample_rate_hz,
-                                               int* channels) {
+                                               size_t* channels) {
   switch (codec_type) {
 #ifdef WEBRTC_CODEC_PCM16
     case acm2::ACMCodecDB::kPCM16B: