fix(animations): always cleanup players after they have finished internally (#13334)

Closes #13333
Closes #13334

modules/@angular/core/test/linker/animation_view_context_spec.ts

@@ -0,0 +1,61 @@
+/**
+ * @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 {el} from '@angular/platform-browser/testing/browser_util';
+
+import {NoOpAnimationPlayer} from '../../src/animation/animation_player';
+import {AnimationViewContext} from '../../src/linker/animation_view_context';
+import {fakeAsync, flushMicrotasks} from '../../testing';
+import {describe, expect, iit, it} from '../../testing/testing_internal';
+
+export function main() {
+  describe('AnimationViewContext', function() {
+    let viewContext: AnimationViewContext;
+    let elm: any;
+    beforeEach(() => {
+      viewContext = new AnimationViewContext();
+      elm = el('<div></div>');
+    });
+
+    function getPlayers() { return viewContext.getAnimationPlayers(elm); }
+
+    it('should remove the player from the registry once the animation is complete',
+       fakeAsync(() => {
+         const player = new NoOpAnimationPlayer();
+
+         expect(getPlayers().length).toEqual(0);
+         viewContext.queueAnimation(elm, 'someAnimation', player);
+         expect(getPlayers().length).toEqual(1);
+         player.finish();
+         expect(getPlayers().length).toEqual(0);
+       }));
+
+    it('should not remove a follow-up player from the registry if another player is queued',
+       fakeAsync(() => {
+         const player1 = new NoOpAnimationPlayer();
+         const player2 = new NoOpAnimationPlayer();
+
+         viewContext.queueAnimation(elm, 'someAnimation', player1);
+         expect(getPlayers().length).toBe(1);
+         expect(getPlayers()[0]).toBe(player1);
+
+         viewContext.queueAnimation(elm, 'someAnimation', player2);
+         expect(getPlayers().length).toBe(1);
+         expect(getPlayers()[0]).toBe(player2);
+
+         player1.finish();
+
+         expect(getPlayers().length).toBe(1);
+         expect(getPlayers()[0]).toBe(player2);
+
+         player2.finish();
+
+         expect(getPlayers().length).toBe(0);
+       }));
+  });
+}