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

ios/clean/chrome/browser/browser_coordinator_unittest.mm

 // Copyright 2017 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/browser_coordinator+internal.h"
 #import "ios/clean/chrome/browser/browser_coordinator.h"
 
 #import "ios/shared/chrome/browser/coordinator_context/coordinator_context.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/gtest_mac.h"
@@ skipping 13 matching lines @@
 
 - (instancetype)init {
   if (!(self = [super init]))
     return nil;
 
   _viewController = [[UIViewController alloc] init];
   return self;
 }
 
 - (void)stop {
+  [super stop];
   if (self.stopHandler)
     self.stopHandler();
 }
 
 @end
 
 @interface NonOverlayableCoordinator : TestCoordinator
 @end
 
 @implementation NonOverlayableCoordinator
@@ skipping 87 matching lines @@
       [[NonOverlayableCoordinator alloc] init];
   TestCoordinator* thirdOverlay = [[TestCoordinator alloc] init];
 
   EXPECT_FALSE([noOverlays canAddOverlayCoordinator:thirdOverlay]);
   EXPECT_FALSE(thirdOverlay.overlaying);
   [noOverlays addOverlayCoordinator:thirdOverlay];
   EXPECT_FALSE(thirdOverlay.overlaying);
 }
 
 }  // namespace