Bug 1520075 - Store the window reference on the child actors as a weak reference. r=mconley

Differential Revision: https://phabricator.services.mozilla.com/D19850

--HG--
extra : moz-landing-system : lando

toolkit/modules/ActorManagerChild.jsm

@@ -63,6 +63,8 @@ class Dispatcher {
     for (let topic of this.observers.keys()) {
       Services.obs.removeObserver(this, topic);
     }
+
+    this.mm.removeEventListener("unload", this);
   }
 
   get window() {
@@ -187,7 +189,7 @@ class SingletonDispatcher extends Dispatcher {
     window.addEventListener("pageshow", this, {mozSystemGroup: true});
     window.addEventListener("pagehide", this, {mozSystemGroup: true});
 
-    this._window = window;
+    this._window = Cu.getWeakReference(window);
     this.listeners = [];
   }
 
@@ -227,7 +229,7 @@ class SingletonDispatcher extends Dispatcher {
   }
 
   get window() {
-    return this._window;
+    return this._window.get();
   }
 
   handleEvent(event) {