fix(animations): microtasks should not be timeouts (#14687)

modules/@angular/animations/src/util.ts

@@ -6,6 +6,5 @@
  * found in the LICENSE file at https://angular.io/license
  */
 export function scheduleMicroTask(cb: () => any) {
-  // FIXME
-  setTimeout(cb, 0);
+  Promise.resolve(null).then(cb);
 }

modules/@angular/animations/test/util_spec.ts

@@ -0,0 +1,24 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {scheduleMicroTask} from '../src/util';
+
+export function main() {
+  describe('util', () => {
+    it('should schedule a microtask and not call an async timeout', (done) => {
+      let count = 0;
+      scheduleMicroTask(() => count++);
+
+      expect(count).toEqual(0);
+      Promise.resolve(null).then(() => {
+        expect(count).toEqual(1);
+        done();
+      });
+      expect(count).toEqual(0);
+    });
+  });
+}