fix(repeat): preserve Subscriber chain in repeat()

Fix repeat() operator to add its own Subscriber to the destination Subscriber, in order to avoid
breaking unsubscription chains.

For issue #875.

src/operator/repeat.ts

@@ -28,7 +28,8 @@ class FirstRepeatSubscriber<T> extends Subscriber<T> {
  constructor(public destination: Subscriber<T>,
  private count: number,
  private source: Observable<T>) {
- super(null);
+ super();
+ destination.add(this);
  this.lastSubscription = this;
  }
 
@@ -56,20 +57,23 @@ class FirstRepeatSubscriber<T> extends Subscriber<T> {
  }
 
  resubscribe(count: number): void {
- this.lastSubscription.unsubscribe();
+ const { destination, lastSubscription } = this;
+ destination.remove(lastSubscription);
+ lastSubscription.unsubscribe();
  if (count - 1 === 0) {
- this.destination.complete();
+ destination.complete();
  } else {
  const nextSubscriber = new MoreRepeatSubscriber(this, count - 1);
  this.lastSubscription = this.source.subscribe(nextSubscriber);
+ destination.add(this.lastSubscription);
  }
  }
 }
 
 class MoreRepeatSubscriber<T> extends Subscriber<T> {
  constructor(private parent: FirstRepeatSubscriber<T>,
  private count: number) {
- super(null);
+ super();
  }
 
  _next(value: T): void {