Fixed sounds registration in SoundsManager.

BUG=321335
TEST=manual tests on Lumpy, media_unittests:SoundsManager*

Review URL: https://codereview.chromium.org/108403003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240176 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240176