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

ios/chrome/browser/ui/history/tab_history_view_controller.h

 // Copyright 2014 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_HISTORY_TAB_HISTORY_VIEW_CONTROLLER_H_
 #define IOS_CHROME_BROWSER_UI_HISTORY_TAB_HISTORY_VIEW_CONTROLLER_H_
 
 #import <UIKit/UIKit.h>
 
 // View controller for displaying a list of CRWSessionEntry objects in a table.
 @interface TabHistoryViewController : UICollectionViewController
 
 // TODO(crbug.com/546355): Convert this class to use an array of
 //    NavigationEntries.
-@property(nonatomic, retain) NSArray* sessionEntries;
+@property(nonatomic, strong) NSArray* sessionEntries;
 
 // Returns the optimal height needed to display the session entries.
 // The height returned is usually less than the |suggestedHeight| unless
 // the last row of the table puts the height just over the |suggestedHeight|.
 // If the session entries table is taller than the |suggestedHeight| by at least
 // one row, the last visible session entry will be shown partially so the user
 // can tell that the table is scrollable.
 - (CGFloat)optimalHeight:(CGFloat)suggestedHeight;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_HISTORY_TAB_HISTORY_VIEW_CONTROLLER_H_