Enable Screen Orientation API.

This CL also gives a way to disable the API from the embedder. The
intent is to disable the API on Windosw 8 Metro until it can be
supported. See http://crbug.com/400846.

BUG=162827

Review URL: https://codereview.chromium.org/440963004

git-svn-id: svn://svn.chromium.org/blink/trunk@179597 bbb929c8-8fbe-4397-9dbb-9b2b20218538