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

ios/clean/chrome/browser/ui/toolbar/toolbar_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/toolbar/toolbar_coordinator.h"
 
@@ skipping 33 matching lines @@
 }
 
 - (void)start {
   self.viewController = [[ToolbarViewController alloc] init];
   self.viewController.toolbarCommandHandler = self;
   self.mediator.consumer = self.viewController;
 
   [self.context.baseViewController presentViewController:self.viewController
                                                 animated:self.context.animated
                                               completion:nil];
+  [super start];
 }
 
 #pragma mark - ToolbarCommands
 
 - (void)showToolsMenu {
   ToolsCoordinator* toolsCoordinator = [[ToolsCoordinator alloc] init];
   toolsCoordinator.toolbarCommandHandler = self;
   [self addChildCoordinator:toolsCoordinator];
   [toolsCoordinator start];
   self.toolsMenuCoordinator = toolsCoordinator;
 }
 
 - (void)closeToolsMenu {
   [self.toolsMenuCoordinator stop];
   [self removeChildCoordinator:self.toolsMenuCoordinator];
 }
 
 @end