Look up notifier in the registry

Extension modules should look up implementations of particular
interfaces in the application registry, not by magic keyword on the
application itself.

Author: nickstenning

src/ext/unsupported.js

@@ -45,15 +45,24 @@ function unsupported() {
     // Reference as exports.checkSupport so that we can stub it for testing.
     var result = exports.checkSupport();
 
+    function fallback(message, severity) {
+        if (severity === annotator.notification.ERROR) {
+            console.error(message);
+            return;
+        }
+        console.log(message);
+    }
+
     function notifyUser(app) {
         if (result.supported) {
             return;
         }
+        var notify = app.registry.queryUtility('notifier') || fallback;
         var msg;
         msg = _t("Sorry, Annotator does not currently support your browser! ");
         msg += _t("Errors: ");
         msg += result.errors.join(", ");
-        app.notify(msg);
+        notify(msg);
     }
 
     return {

test/spec/ext/unsupported_spec.js

@@ -59,12 +59,16 @@ describe("unsupported.checkSupport()", function () {
 
 
 describe('annotator.ext.unsupported module', function () {
+    var mockNotify;
     var mockApp;
     var sandbox = sinon.sandbox.create();
 
     beforeEach(function () {
+        mockNotify = sandbox.stub();
         mockApp = {
-            notify: sandbox.stub()
+            registry: {
+                queryUtility: sandbox.stub().withArgs('notifier').returns(mockNotify)
+            }
         };
 
         sandbox.stub(unsupported, 'checkSupport').returns({
@@ -82,7 +86,7 @@ describe('annotator.ext.unsupported module', function () {
         plugin.start(mockApp);
 
         sinon.assert.calledWith(
-            mockApp.notify,
+            mockNotify,
             sinon.match('widgets are discombobulated')
         );
     });