Turn on audio mixer by default.

media/audio/audio_manager_base.cc

 // Copyright (c) 2012 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/audio_manager_base.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/message_loop_proxy.h"
 #include "base/threading/thread.h"
@@ skipping 125 matching lines @@
 AudioOutputStream* AudioManagerBase::MakeAudioOutputStreamProxy(
     const AudioParameters& params) {
   DCHECK(GetMessageLoop()->BelongsToCurrentThread());
 
   scoped_refptr<AudioOutputDispatcher>& dispatcher =
       output_dispatchers_[params];
   if (!dispatcher) {
     base::TimeDelta close_delay =
         base::TimeDelta::FromSeconds(kStreamCloseDelaySeconds);
     const CommandLine* cmd_line = CommandLine::ForCurrentProcess();
-    if (cmd_line->HasSwitch(switches::kEnableAudioMixer)) {
+    if (!cmd_line->HasSwitch(switches::kDisableAudioMixer)) {
       dispatcher = new AudioOutputMixer(this, params, close_delay);
     } else {
       dispatcher = new AudioOutputDispatcherImpl(this, params, close_delay);
     }
   }
   return new AudioOutputProxy(dispatcher);
 }
 
 bool AudioManagerBase::CanShowAudioInputSettings() {
   return false;
@@ skipping 76 matching lines @@
       // So, better crash now than later.
       DCHECK(dispatcher->HasOneRef()) << "AudioOutputProxies are still alive";
       dispatcher = NULL;
     }
   }
 
   output_dispatchers_.clear();
 }
 
 }  // namespace media