This is the first step in making it possible to return remote WindowProxy
objects from window.open() and related APIs.
This patch also incidentally fixes a bug where getContentWindowOrOpenURI
returned the top-level browser window rather than the new content window when
passed OPEN_NEWWINDOW for the `aWhere` parameter. This was not the expected
behavior, and was a potentially major footgun for any new users who expected
to always get the content window for the URL they were loading, rather than
sometimes getting a chrome browser window instead.
For now, that case just returns null, which is only a minor footgun, rather
than the major one we had before.
Differential Revision: https://phabricator.services.mozilla.com/D35688
--HG--
extra : moz-landing-system : lando
22592538f5