Resolve screen.orientation.lock() promise with undefined.

This is following the current state of the specification.

BUG=162827

Review URL: https://codereview.chromium.org/400703003

git-svn-id: svn://svn.chromium.org/blink/trunk@178406 bbb929c8-8fbe-4397-9dbb-9b2b20218538