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

ios/chrome/browser/ui/side_swipe/history_side_swipe_provider.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.
 
 #import "ios/chrome/browser/ui/side_swipe/history_side_swipe_provider.h"
 
+#include "ios/chrome/browser/tabs/tab.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface HistorySideSwipeProvider () {
   // Keep a reference to detach before deallocing.
-  TabModel* _tabModel;  // weak
+  __weak TabModel* _tabModel;  // weak
 }
 
 @end
 
 @implementation HistorySideSwipeProvider
 - (instancetype)initWithTabModel:(TabModel*)tabModel {
   self = [super init];
   if (self) {
     _tabModel = tabModel;
   }
@@ skipping 18 matching lines @@
 
 - (UIImage*)paneIcon {
   return [UIImage imageNamed:@"side_swipe_navigation_back"];
 }
 
 - (BOOL)rotateForwardIcon {
   return YES;
 }
 
 @end