Fix AudioScheduler and VideoScheduler creation.

The schedulers post startup tasks to a secondary thread, running the risk that
the secondary thread will them down before the caller has had a chance to take
a reference to them.

BUG=164795


Review URL: https://chromiumcodereview.appspot.com/11474015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171925 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed