fix(dart): don't instantiate abstract directive.

Directive is an abstract class, so it should not
be instantiated directly in tests.

modules/angular2/test/core/annotations/annotations_spec.js

@@ -1,21 +1,25 @@
 import {ddescribe, describe, it, iit, expect, beforeEach} from 'angular2/test_lib';
 import {Directive, onChange} from 'angular2/src/core/annotations/annotations';
 
+class DummyDirective extends Directive {
+  constructor({lifecycle = []} = {}) { super({lifecycle}); }
+}
+
 export function main() {
   describe("Directive", () => {
     describe("lifecycle", () => {
       it("should be false when no lifecycle specified", () => {
-        var d = new Directive();
+        var d = new DummyDirective();
         expect(d.hasLifecycleHook(onChange)).toBe(false);
       });
 
       it("should be false when the lifecycle does not contain the hook", () => {
-        var d = new Directive({lifecycle:[]});
+        var d = new DummyDirective({lifecycle:[]});
         expect(d.hasLifecycleHook(onChange)).toBe(false);
       });
 
       it("should be true otherwise", () => {
-        var d = new Directive({lifecycle:[onChange]});
+        var d = new DummyDirective({lifecycle:[onChange]});
         expect(d.hasLifecycleHook(onChange)).toBe(true);
       });
     });