Add chromium support for MediaStreamAudioDestinationNode

      We add smarts into MediaStreamDependencyFactory::CreateNativeLocalMediaStream()
to handle MediaStreams originating from WebAudio.

Please see companion WebKit patches:
https://bugs.webkit.org/show_bug.cgi?id=101815
https://bugs.webkit.org/show_bug.cgi?id=106053

BUG=none
TEST=manual test
http://www.corp.google.com/~henrika/WebAudio/MediaStreamAudioDestinationNode.html

Review URL: https://chromiumcodereview.appspot.com/11369171

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@177330 0039d316-1c4b-4281-b951-d872f2087c98