loadURIDelegate and webBrowserChrome are set on the docShell inside frame scripts (here on Desktop and here on GeckoView). We need a way to let docShell discover these delegates when they are implented as an Actor.

kmag suggested we use a named Actor that gets loaded by the docShell whenever it needs to use the property.

Note we should probably allow explicitly setting webBrowserChrome, at least for now, and fall back to looking up an actor only if hasn't already been set on the top-level content docshell.

Ideally, I think we want to move to using the same actor everywhere, but for the moment, we still use something slightly different for extension panels, and in-process tabs do some magic to use XULBrowserWindow for their nsIWebBrowserChrome3.

Thanks Agi for taking this.

firefox69=wontfix because we don't need to uplift this fix to Beta.

This allows querying the actor for interfaces implemented in JS.

Adding this bug to GV's September sprint. Agi says his patches are waiting for review.

When DelegatedQueryInterface is called on a XPCWrappedJS that has an aggregated
native object (e.g. in the case of a JS-implemented class that extends a native
object like JSWindowActor), we end up calling QueryInterface on the native
object, even though we know already that the interface is implemented on the JS
object.

To fix this, we bypass the native object QI call by calling
AggregatedQueryInterface.

https://hg.mozilla.org/mozilla-central/rev/84bd781b0b8c
https://hg.mozilla.org/mozilla-central/rev/3626cfe835ee
https://hg.mozilla.org/mozilla-central/rev/c6ac454bfe48
https://hg.mozilla.org/mozilla-central/rev/205690af8630