Use WebScreenInfo for window.orientation.

Using WebScreenInfo in window.orientation will allow having a valid
value at any time, even when the renderer process just got created
because WebScreenInfo is passed at creation time.

Furthermore, it removes the need to pass the orientation value when
notifying Blink that a screen orientation happened.

BUG=154478

Review URL: https://codereview.chromium.org/267423002

git-svn-id: svn://svn.chromium.org/blink/trunk@173532 bbb929c8-8fbe-4397-9dbb-9b2b20218538