BrowserCoordinator stops its children.

ios/clean/chrome/browser/ui/tab/tab_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.
 
 #import "ios/clean/chrome/browser/ui/tab/tab_coordinator.h"
 
 #include <memory>
 
 #include "base/mac/foundation_util.h"
 #include "base/memory/ptr_util.h"
@@ skipping 81 matching lines @@
   if (self.webState->GetLastCommittedURL() == GURL(kChromeUINewTabURL)) {
     self.viewController.contentViewController =
         self.ntpCoordinator.viewController;
   }
 
   [super start];
 }
 
 - (void)stop {
   [super stop];
-  // PLACEHOLDER: Stop child coordinators here for now. We might deal with this
-  // differently later on.
-  for (BrowserCoordinator* child in self.children) {
-    [child stop];
-  }
   _webStateObserver.reset();
   [self.browser->dispatcher() stopDispatchingToTarget:self];
 }
 
 - (void)childCoordinatorDidStart:(BrowserCoordinator*)childCoordinator {
   if ([childCoordinator isKindOfClass:[ToolbarCoordinator class]]) {
     self.viewController.toolbarViewController = childCoordinator.viewController;
   } else if ([childCoordinator isKindOfClass:[WebCoordinator class]] ||
              [childCoordinator isKindOfClass:[NTPCoordinator class]]) {
     self.viewController.contentViewController = childCoordinator.viewController;
@@ skipping 77 matching lines @@
   return animator;
 }
 
 #pragma mark - TabCommands
 
 - (void)loadURL:(web::NavigationManager::WebLoadParams)params {
   self.webState->GetNavigationManager()->LoadURLWithParams(params);
 }
 
 @end