The menuitem used to be only included in the markup for the non-browser window
case. This changes it to include it as a hidden <menuitem> for the browser window
case, and then unhide it for the non-browser window case.
MozReview-Commit-ID: 8tY3GiTFmqe
It's currently in macWindow.inc.xul which means it gets created for
all non-browser windows, but it's only ever set up for the hidden window.
MozReview-Commit-ID: LeXjKihPRYB
Move all of the overlay pieces into an include file except for the
DTD's that could not be put there. Inline the DTD's into the files
where they were used. Update comments in macWindow.inc.xul and browser.xul
to more accurately reflect the current state.
MozReview-Commit-ID: HZIeSf29Yl
