Exposed virtual keyboard control in kiosk mode.

BUG=343670
TEST=expanded ExtensionApiTest.ChromeOSInfoPrivateTest

Review URL: https://codereview.chromium.org/164993003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251597 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251597