fix(animations): ensure parent animations are triggered before children (#11201)

modules/@angular/core/src/animation/animation_queue.ts

@@ -0,0 +1,25 @@
+/**
+ * @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 {AnimationPlayer} from './animation_player';
+
+var _queuedAnimations: AnimationPlayer[] = [];
+
+/** @internal */
+export function queueAnimation(player: AnimationPlayer) {
+  _queuedAnimations.push(player);
+}
+
+/** @internal */
+export function triggerQueuedAnimations() {
+  for (var i = 0; i < _queuedAnimations.length; i++) {
+    var player = _queuedAnimations[i];
+    player.play();
+  }
+  _queuedAnimations = [];
+}