Bug 1483600 - Notify "tab-content-frameloader-created" in GeckoView content script. r=jchen

Differential Revision: https://phabricator.services.mozilla.com/D3546

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

mobile/android/chrome/geckoview/GeckoViewContent.js

@@ -34,6 +34,9 @@ class GeckoViewContent extends GeckoViewContentModule {
                                            this);
     this.messageManager.addMessageListener("GeckoView:ZoomToInput",
                                            this);
+
+    // Notify WebExtension process script that this tab is ready for extension content to load.
+    Services.obs.notifyObservers(this.messageManager, "tab-content-frameloader-created");
   }
 
   onEnable() {