This will be useful as both an ID for PWindowGlobal, as well as a mechanism for
taking advantage of already synchronized information. As an example, LoadInfo
objects contain the inner window IDs of the window requesting the load, which
can now be used to obtain a reference to the corresponding WindowGlobalParent
in the parent process.
Differential Revision: https://phabricator.services.mozilla.com/D9396
This serves 2 purposes:
1. Provides an object corresponding to an inner window which Chrome JS can hold onto.
2. Provides the object to JS which Chrome JS per-window actors will be attached to.
3. Provides useful information to Chrome JS in the parent process.
Differential Revision: https://phabricator.services.mozilla.com/D9394