Revert r157378 as it caused WebRTC to dereference null pointers when restarting a call.

I've kept my unit test changes intact but disabled until I get a proper fix.

BUG=147499,150805
TBR=henrika

Review URL: https://codereview.chromium.org/10946040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@157626 0039d316-1c4b-4281-b951-d872f2087c98
void AudioOutputDevice::Start() {
  DCHECK(callback_) << "Initialize hasn't been called";
  message_loop()->PostTask(FROM_HERE,
      base::Bind(&AudioOutputDevice::CreateStreamOnIOThread, this,
                 audio_parameters_, input_channels_));
}

void AudioOutputDevice::Start() {
  DCHECK(callback_) << "Initialize hasn't been called";
  message_loop()->PostTask(FROM_HERE,
      base::Bind(&AudioOutputDevice::CreateStreamOnIOThread, this,
                 audio_parameters_, input_channels_));
}
