Add test to make sure ChromeVox speaks when we type in the omnibox.

BUG=339902
R=plundblad@chromium.org

Review URL: https://codereview.chromium.org/175593003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252885 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252885