[Autofill, Sync] Update the AutofillTable API to return dates directly, not as vectors.

BUG=118696
TEST=unit_tests
R=estade@chromium.org

Review URL: https://codereview.chromium.org/173493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254450 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254450