Update Enhanced Playback dialog string.

R=ericde@chromium.org
TBR=engedy@chromium.org
BUG=344643

Review URL: https://codereview.chromium.org/171483002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251881 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251881