Convert channel counts to size_t.

webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc

Index: webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc b/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
index ef48a48d94d275a9fad0fdeec7adc2e21280e912..6f82a96ee508414a488df94824e48e6da95bbab7 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_unittest_oldapi.cc
@@ -300,7 +300,7 @@ TEST_F(AudioCodingModuleTestOldApi, VerifyOutputFrame) {
   EXPECT_EQ(0, acm_->PlayoutData10Ms(kSampleRateHz, &audio_frame));
   EXPECT_EQ(id_, audio_frame.id_);
   EXPECT_EQ(0u, audio_frame.timestamp_);
-  EXPECT_GT(audio_frame.num_channels_, 0);
+  EXPECT_GT(audio_frame.num_channels_, 0u);
   EXPECT_EQ(static_cast<size_t>(kSampleRateHz / 100),
             audio_frame.samples_per_channel_);
   EXPECT_EQ(kSampleRateHz, audio_frame.sample_rate_hz_);