Deprecate openDatabase and openDatabaseSync in workers.

We show console message when they are used.

Intent to deprecate: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/2SWnbXAL7Wg

BUG=397429

Review URL: https://codereview.chromium.org/417103002

git-svn-id: svn://svn.chromium.org/blink/trunk@178954 bbb929c8-8fbe-4397-9dbb-9b2b20218538