[ObjC ARC] Converts ios/chrome/browser/ui/side_swipe:side_swipe to ARC.

ios/chrome/browser/ui/side_swipe/side_swipe_navigation_view.h

 // Copyright 2015 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_SIDE_SWIPE_SIDE_SWIPE_NAVIGATION_VIEW_H_
 #define IOS_CHROME_BROWSER_UI_SIDE_SWIPE_SIDE_SWIPE_NAVIGATION_VIEW_H_
 
 #import <UIKit/UIKit.h>
 
 @class SideSwipeGestureRecognizer;
 
 // Accessory view showing forward or back arrow while the main target view
 // is dragged from side to side.
 @interface SideSwipeNavigationView : UIView
 
-@property(nonatomic, assign) UIView* targetView;
+@property(nonatomic, weak) UIView* targetView;
 
 // Initialize with direction.
 - (instancetype)initWithFrame:(CGRect)frame
                 withDirection:(UISwipeGestureRecognizerDirection)direction
                   canNavigate:(BOOL)canNavigate
                         image:(UIImage*)image
                 rotateForward:(BOOL)rotateForward;
 
 // Update views for latest gesture, and call completion blocks whether
 // |threshold| is met.
 - (void)handleHorizontalPan:(SideSwipeGestureRecognizer*)gesture
      onOverThresholdCompletion:(void (^)(void))onOverThresholdCompletion
     onUnderThresholdCompletion:(void (^)(void))onUnderThresholdCompletion;
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_SIDE_SWIPE_SIDE_SWIPE_NAVIGATION_VIEW_H_