Changing plugin setwindow() to use page coordinate

Changing plugin setwindow() to use page coordinate
instead of frame as it is what Flash expects. For
other port like Mac, it passes the window coordinate
to the plugin. In Android, plugin always sees the
full page and we use the visible screen rect to
indicate whether it is visible.

Change to use page coordinate across PluginView and
PluginWidget for consistency. This should fix the
problem Ben saw with plugin inside iframe (which is
caused by a race condition) and the cnnn ad problem
Adobe has.