Fix the output device selection introduced by 163343002.

It corrects a mistake which does not assign the output device id to the member of the dispatcher.

NOTRY=true

BUG=344818
TEST=http://localhost:8080/hangout_services_test.html works with device selection.
R=joi@chromium.org

Review URL: https://codereview.chromium.org/172243003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252025 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252025