e97c582e3f
DocShells are associated with outer DOM Windows, rather than Documents, so having the getter on the document is a bit odd to begin with. But it's also considerably less convenient, since most of the times when we want a docShell from JS, we're dealing most directly with a window, and have to detour through the document to get it. MozReview-Commit-ID: LUj1H9nG3QL