Add Undefined value to WebScreenOrientationType.

ScreenOrientation object will compute the orientation type based on the
information it has if the orientation type is set to undefined in the
WebScreenInfo instance.

BUG=162827

Review URL: https://codereview.chromium.org/241333003

git-svn-id: svn://svn.chromium.org/blink/trunk@171903 bbb929c8-8fbe-4397-9dbb-9b2b20218538