Changed the default for tap-to-click to true.

BUG=chromium-os:9342
TEST=Check that tap-to-click is on on login screen and for users with default setting.

Review URL: http://codereview.chromium.org/5146003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@66612 0039d316-1c4b-4281-b951-d872f2087c98