Clean up: remove a non-required @required.

ios/chrome/browser/ui/stack_view/stack_view_controller.h

 // Copyright 2012 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.
 
 #ifndef IOS_CHROME_BROWSER_UI_STACK_VIEW_STACK_VIEW_CONTROLLER_H_
 #define IOS_CHROME_BROWSER_UI_STACK_VIEW_STACK_VIEW_CONTROLLER_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher.h"
 #include "ui/base/page_transition_types.h"
 
 class GURL;
 @class Tab;
 @class TabModel;
 
 // A protocol used by the StackViewController for test purposes.
 @protocol StackViewControllerTestDelegate
-@required
 // Informs the delegate that the show tab animation starts.
 - (void)stackViewControllerShowWithSelectedTabAnimationDidStart;
 // Informs the delegate that the show tab animation finished.
 - (void)stackViewControllerShowWithSelectedTabAnimationDidEnd;
 // Informs the delegate that the preload of card views finished.
 - (void)stackViewControllerPreloadCardViewsDidEnd;
 @end
 
 // Controller for the tab-switching UI displayed as a stack of tabs.
 @interface StackViewController : UIViewController<TabSwitcher>
@@ skipping 40 matching lines @@
 // |position| with |transition|. Otherwise, simply returns nil.
 // If |position| == NSNotFound the tab will be added at the end of the stack.
 - (Tab*)dismissWithNewTabAnimationToModel:(TabModel*)targetModel
                                   withURL:(const GURL&)url
                                   atIndex:(NSUInteger)position
                                transition:(ui::PageTransition)transition;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_STACK_VIEW_STACK_VIEW_CONTROLLER_H_