Coordinators: let the presenting view controller dismiss.

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.
 
 // ======                        New Architecture                         =====
 // =         This code is only used in the new iOS Chrome architecture.       =
 // ============================================================================
 
 #import "ios/clean/chrome/browser/ui/tab/tab_coordinator.h"
 
@@ skipping 58 matching lines @@
 
   self.viewController.toolbarViewController = toolbarCoordinator.viewController;
   self.viewController.contentViewController = webCoordinator.viewController;
 
   [self.baseViewController presentViewController:self.viewController
                                         animated:self.context.animated
                                       completion:nil];
 }
 
 - (void)stop {
-  [self.viewController dismissViewControllerAnimated:self.context.animated
-                                          completion:nil];
+  [self.viewController.presentingViewController
+      dismissViewControllerAnimated:self.context.animated
+                         completion:nil];
   _webStateObserver.reset();
 }
 
 - (BOOL)canAddOverlayCoordinator:(BrowserCoordinator*)overlayCoordinator {
   // This coordinator will always accept overlay coordinators.
   return YES;
 }
 
 #pragma mark - Experiment support
 
@@ skipping 23 matching lines @@
 - (id<UIViewControllerAnimatedTransitioning>)
 animationControllerForDismissedController:(UIViewController*)dismissed {
   ZoomTransitionAnimator* animator = [[ZoomTransitionAnimator alloc] init];
   animator.presenting = NO;
   animator.presentationKey = self.presentationKey;
   [animator selectDelegate:@[ dismissed.presentingViewController ]];
   return animator;
 }
 
 @end