[ARC] Converts part of ios/web to ARC.

ios/web/web_state/ui/crw_generic_content_view.mm

 // 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.
 
 #import "ios/web/public/web_state/ui/crw_generic_content_view.h"
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface CRWGenericContentView () {
   // The size of the view's bounds at the last call to |-layoutSubviews|.
   CGSize _lastLayoutSize;
   // Backing objectect for |self.scrollView|.
   base::scoped_nsobject<UIScrollView> _scrollView;
   // Backing object for |self.view|.
   base::scoped_nsobject<UIView> _view;
 }
 
 @end
 
 @implementation CRWGenericContentView
 
 - (instancetype)initWithView:(UIView*)view {
   self = [super initWithFrame:CGRectZero];
   if (self) {
     DCHECK(view);
     _lastLayoutSize = CGSizeZero;
-    _view.reset([view retain]);
+    _view.reset(view);
     _scrollView.reset([[UIScrollView alloc] initWithFrame:CGRectZero]);
     [self addSubview:_scrollView];
     [_scrollView addSubview:_view];
     [_scrollView setBackgroundColor:[_view backgroundColor]];
   }
   return self;
 }
 
 - (instancetype)initWithCoder:(NSCoder*)decoder {
   NOTREACHED();
@@ skipping 54 matching lines @@
     viewSize.height = CGRectGetHeight(contentRect) + singlePixel;
   }
   self.scrollView.contentSize = viewSize;
 }
 
 - (BOOL)isViewAlive {
   return YES;
 }
 
 @end