Fix compile error in audio_manager_cras when dcheck_always_on=true

media/audio/cras/audio_manager_cras.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/audio/cras/audio_manager_cras.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 74 matching lines @@
       return device.mic_positions;
     }
   }
   return "";
 }
 
 // Process |device_list| that two shares the same dev_index by creating a
 // virtual device name for them.
 void ProcessVirtualDeviceName(AudioDeviceNames* device_names,
                               const chromeos::AudioDeviceList& device_list) {
-  DCHECK_EQ(2, device_list.size());
+  DCHECK_EQ(2U, device_list.size());
   if (device_list[0].type == chromeos::AUDIO_TYPE_LINEOUT ||
       device_list[1].type == chromeos::AUDIO_TYPE_LINEOUT) {
     device_names->emplace_back(kHeadphoneLineOutVirtualDevice,
                                base::Uint64ToString(device_list[0].id));
   } else if (device_list[0].type == chromeos::AUDIO_TYPE_INTERNAL_SPEAKER ||
              device_list[1].type == chromeos::AUDIO_TYPE_INTERNAL_SPEAKER) {
     device_names->emplace_back(kInternalOutputVirtualDevice,
                                base::Uint64ToString(device_list[0].id));
   } else {
     DCHECK(device_list[0].type == chromeos::AUDIO_TYPE_INTERNAL_MIC ||
@@ skipping 257 matching lines @@
 
 bool AudioManagerCras::IsDefault(const std::string& device_id, bool is_input) {
   AudioDeviceNames device_names;
   GetAudioDeviceNamesImpl(is_input, &device_names);
   DCHECK(!device_names.empty());
   const AudioDeviceName& device_name = device_names.front();
   return device_name.unique_id == device_id;
 }
 
 }  // namespace media