gwtquake lets the renderer create > 300 threads (one per audio element?), and eventually thread creation fails. This CL makes the media code more robust against thread creation failure (currently, it just crashes the renderer).

The Real Fix probably is to have a thread pool for media stuff instead of one thread per media object. And maybe threads just leak under some circumstances. I will file a follow-up bug for that case, hopefully with a reduced test case.

BUG=53867,61293
TEST=Completing the first level in gwtquake shouldn't crash the renderer.

Review URL: http://codereview.chromium.org/5362003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@67824 0039d316-1c4b-4281-b951-d872f2087c98