Child coordinators notify their parent upon -start and -stop.

ios/clean/chrome/browser/ui/web_contents/web_coordinator.mm

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // ======                        New Architecture                         =====
 // =         This code is only used in the new iOS Chrome architecture.       =
 // ============================================================================
 
 #import "ios/clean/chrome/browser/ui/web_contents/web_coordinator.h"
 
@@ skipping 32 matching lines @@
 - (void)start {
   self.viewController = [[WebContentsViewController alloc] init];
   self.mediator.consumer = self.viewController;
 
   // Reminder: this is a no-op if |baseViewController| is nil, for example
   // when this coordinator's view controller will be contained instead of
   // presented.
   [self.context.baseViewController presentViewController:self.viewController
                                                 animated:self.context.animated
                                               completion:nil];
+  [super start];
 }
 
 - (void)stop {
+  [super stop];
   // PLACEHOLDER: This is how the webUsageEnabled is set to false. Find a
   // better way in the future.
   self.mediator.webState = nullptr;
 }
 
 @end