Bug 1581925 - Part 2: Use {chrome/content}-document-global-created topic to create SpecialPowers actor, r=kmag

This replaces the old DOMWindowCreated event, and allows SpecialPowers to still
be instantiated for each new chrome document.

Differential Revision: https://phabricator.services.mozilla.com/D47337

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

testing/specialpowers/api.js

@@ -38,9 +38,10 @@ this.specialpowers = class extends ExtensionAPI {
       includeChrome: true,
       child: {
         moduleURI: "resource://specialpowers/SpecialPowersChild.jsm",
-        events: {
-          DOMWindowCreated: {},
-        },
+        observers: [
+          "chrome-document-global-created",
+          "content-document-global-created",
+        ],
       },
       parent: {
         moduleURI: "resource://specialpowers/SpecialPowersParent.jsm",

testing/specialpowers/content/SpecialPowersChild.jsm

@@ -187,9 +187,9 @@ class SpecialPowersChild extends JSWindowActorChild {
     this._extensionListeners = null;
   }
 
-  handleEvent(aEvent) {
-    // We don't actually care much about the "DOMWindowCreated" event.
-    // We only listen to it to force creation of the actor.
+  observe(aSubject, aTopic, aData) {
+    // Ignore the "{chrome/content}-document-global-created" event. It
+    // is only observed to force creation of the actor.
   }
 
   actorCreated() {