Bug 1567341 - Initialize GeckoViewWebExtensions when getting extension-installed. r=esawin

When getting the *-extension-installed messages we should always notify
GeckoViewWebExtension.

This currently works because we always install the test support extension which
causes us to initialize GeckoViewWebExtension. On xpcshel tests, however, there
is no support extension so we need to account for that in GeckoViewStartup.

Differential Revision: https://phabricator.services.mozilla.com/D106319

mobile/android/components/geckoview/GeckoViewStartup.jsm

@@ -94,6 +94,11 @@ class GeckoViewStartup {
             "GeckoView:WebExtension:Uninstall",
             "GeckoView:WebExtension:Update",
           ],
+          observers: [
+            "devtools-installed-addon",
+            "testing-installed-addon",
+            "testing-uninstalled-addon",
+          ],
         });
 
         GeckoViewUtils.addLazyGetter(this, "GeckoViewStorageController", {

mobile/android/modules/geckoview/GeckoViewWebExtension.jsm

@@ -1088,6 +1088,3 @@ var GeckoViewWebExtension = {
 GeckoViewWebExtension.browserActions = new WeakMap();
 // WeakMap[Extension -> PageAction]
 GeckoViewWebExtension.pageActions = new WeakMap();
-Services.obs.addObserver(GeckoViewWebExtension, "devtools-installed-addon");
-Services.obs.addObserver(GeckoViewWebExtension, "testing-installed-addon");
-Services.obs.addObserver(GeckoViewWebExtension, "testing-uninstalled-addon");