Count Web SQL Database usage in Workers.

Web SQL Database is an obsolete specification.
We already count Web SQL Database usage in the DOMWindow context.

BUG=

Review URL: https://codereview.chromium.org/207823004

git-svn-id: svn://svn.chromium.org/blink/trunk@169996 bbb929c8-8fbe-4397-9dbb-9b2b20218538