Make CoreAudio::IsSupported VLOG instead of LOG

This function adds error log spam to unrelated tests.  Changing these
errors to be VLOG like many other calls in this file so that only folks
interested in audio can get these logs.

BUG=339891

Review URL: https://codereview.chromium.org/155823004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250494 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250494