Improve validation when creating audio streams.

BUG=166795
Review URL: https://codereview.chromium.org/11647012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@173981 0039d316-1c4b-4281-b951-d872f2087c98
AudioRendererHost::AudioRendererHost(
    media::AudioManager* audio_manager, MediaObserver* media_observer)
    : audio_manager_(audio_manager),
      media_observer_(media_observer) {
}

AudioRendererHost::AudioRendererHost(
    media::AudioManager* audio_manager, MediaObserver* media_observer)
    : audio_manager_(audio_manager),
      media_observer_(media_observer) {
}
