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

ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_cell.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_TAB_SWITCHER_TAB_SWITCHER_PANEL_CELL_H_
 #define IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_SWITCHER_PANEL_CELL_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_model.h"
@@ skipping 14 matching lines @@
 - (void)deleteButtonPressedForCell:(UICollectionViewCell*)cell;
 
 @end
 
 @interface TabSwitcherSessionCell : UICollectionViewCell
 
 // Returns the cell's identifier used for the cell's re-use.
 + (NSString*)identifier;
 
 // The cell delegate.
-@property(nonatomic, assign) id<SessionCellDelegate> delegate;
+@property(nonatomic, unsafe_unretained) id<SessionCellDelegate> delegate;
 
 @end
 
 // Cell showing information about a local session.
 @interface TabSwitcherLocalSessionCell : TabSwitcherSessionCell
 
 // Returns the top bar of the cell. The top bar holds the favicon and the tab
 // title.
-@property(nonatomic, readonly) UIView* topBar;
+@property(unsafe_unretained, nonatomic, readonly) UIView* topBar;
 
 // Sets the cell's appearance using information in |tab|.
 // The delegate needs to be set before calling this method.
 - (void)setAppearanceForTab:(Tab*)tab cellSize:(CGSize)cellSize;
 
 // PLACEHOLDER: Sets the cell's appearance using information in |title| and
 // |favicon|.
 - (void)setAppearanceForTabTitle:(NSString*)title
                          favicon:(UIImage*)favicon
                         cellSize:(CGSize)cellSize;
@@ skipping 12 matching lines @@
 
 // Sets the cell's title.
 - (void)setTitle:(NSString*)title;
 // Sets the session's URL to obtain the cell's favicon.
 - (void)setSessionGURL:(GURL const&)gurl
       withBrowserState:(ios::ChromeBrowserState*)browserState;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_SWITCHER_PANEL_CELL_H_