Use Promises for screen.lockOrientation().

This change is changing the Blink implementation and adds the Platform
interface but changes in the content layer a required to make it work
fully.

BUG=162827

Review URL: https://codereview.chromium.org/283423005

git-svn-id: svn://svn.chromium.org/blink/trunk@174773 bbb929c8-8fbe-4397-9dbb-9b2b20218538