Convert channel counts to size_t.

talk/media/base/fakemediaengine.h

Index: talk/media/base/fakemediaengine.h
diff --git a/talk/media/base/fakemediaengine.h b/talk/media/base/fakemediaengine.h
index f5b21741d36778c5ded15a1e78226e7b5b599827..149704f92d0cad8b4ddce68e9f7137df6e6ff6d5 100644
--- a/talk/media/base/fakemediaengine.h
+++ b/talk/media/base/fakemediaengine.h
@@ -368,7 +368,7 @@ class FakeVoiceMediaChannel : public RtpHelper<VoiceMediaChannel> {
     void OnData(const void* audio_data,
                 int bits_per_sample,
                 int sample_rate,
-                int number_of_channels,
+                size_t number_of_channels,
                 size_t number_of_frames) override {}
     void OnClose() override { renderer_ = NULL; }
     AudioRenderer* renderer() const { return renderer_; }