[IndexedDB] Origins and document.domain

By my reading, the spec does not clearly specify what the 'origin' should
be.  IDBFactory.open/deleteDatabase say "Let origin be the origin of the
IDBEnvironment used to access this IDBFactory."  The IDL states "Window
implements IDBEnvironment;"  The HTML5 spec, as far as I can tell, does not
define the concept of an origin for a window, but only for a document.

There is another related question here: how should IndexedDB behave in the
presence of modifications to document.domain?

- Kyle