Convert channel counts to size_t.

webrtc/modules/audio_coding/neteq/tools/neteq_external_decoder_test.h

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 36 matching lines @@
   size_t GetOutputAudio(size_t max_length, int16_t* output,
                         NetEqOutputType* output_type);
 
   NetEq* neteq() { return neteq_.get(); }
 
  private:
   NetEqDecoder codec_;
   std::string name_ = "dummy name";
   AudioDecoder* decoder_;
   int sample_rate_hz_;
-  int channels_;
+  size_t channels_;
   rtc::scoped_ptr<NetEq> neteq_;
 };
 
 }  // namespace test
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_TOOLS_NETEQ_EXTERNAL_DECODER_TEST_H_