Extract a DOMWindow interface from LocalDOMWindow and use it in the idl.

This patch switches the bindings code from using LocalDOMWindow to using
the DOMWindow interface. This will allow OOPIF to add a RemoteDOMWindow
class that remote frames can expose to web content.

BUG=425623

Review URL: https://codereview.chromium.org/683013002

git-svn-id: svn://svn.chromium.org/blink/trunk@185067 bbb929c8-8fbe-4397-9dbb-9b2b20218538