Adjust ChromeVox notification strings.

BUG=261451
TEST=Manual

Review URL: https://codereview.chromium.org/112633007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243237 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243237