[NOT FOR REVIEW] Convert channel counts to size_t.

webrtc/modules/audio_processing/voice_detection_impl.cc

 /*
  *  Copyright (c) 2012 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 146 matching lines @@
 
 int VoiceDetectionImpl::InitializeHandle(void* handle) const {
   return WebRtcVad_Init(static_cast<Handle*>(handle));
 }
 
 int VoiceDetectionImpl::ConfigureHandle(void* handle) const {
   return WebRtcVad_set_mode(static_cast<Handle*>(handle),
                             MapSetting(likelihood_));
 }
 
-int VoiceDetectionImpl::num_handles_required() const {
+size_t VoiceDetectionImpl::num_handles_required() const {
   return 1;
 }
 
 int VoiceDetectionImpl::GetHandleError(void* handle) const {
   // The VAD has no get_error() function.
   assert(handle != NULL);
   return apm_->kUnspecifiedError;
 }
 }  // namespace webrtc