feat(animations): make sure animation callback reports the totalTime (#11022)

Closes #11022

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

@@ -0,0 +1,51 @@
+/**
+ * @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
+ */
+
+/**
+ * An instance of this class is returned as an event parameter when an animation
+ * callback is captured for an animation either during the start or done phase.
+ *
+ * ```typescript
+ * @Component({
+ *   host: {
+ *     '[@myAnimationTrigger]': 'someExpression',
+ *     '(@myAnimationTrigger.start)': 'captureStartEvent($event)',
+ *     '(@myAnimationTrigger.done)': 'captureDoneEvent($event)',
+ *   },
+ *   animations: [
+ *     trigger("myAnimationTrigger", [
+ *        // ...
+ *     ])
+ *   ]
+ * })
+ * class MyComponent {
+ *   someExpression: any = false;
+ *   captureStartEvent(event: AnimationTransitionEvent) {
+ *     // the toState, fromState and totalTime data is accessible from the event variable
+ *   }
+ *
+ *   captureDoneEvent(event: AnimationTransitionEvent) {
+ *     // the toState, fromState and totalTime data is accessible from the event variable
+ *   }
+ * }
+ * ```
+ *
+ * @experimental Animation support is experimental.
+ */
+export class AnimationTransitionEvent {
+  public fromState: string;
+  public toState: string;
+  public totalTime: number;
+
+  constructor({fromState, toState,
+               totalTime}: {fromState: string, toState: string, totalTime: number}) {
+    this.fromState = fromState;
+    this.toState = toState;
+    this.totalTime = totalTime;
+  }
+}