Reland of [ObjC ARC] Converts ios/chrome/browser/ui/contextual_search:contextual_search to ARC.

ios/chrome/browser/ui/contextual_search/contextual_search_highlighter_view.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/contextual_search/contextual_search_highlighter_view.h"
 
 #include "base/logging.h"
-#import "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/contextual_search/contextual_search_controller.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation ContextualSearchHighlighterView {
   // Store size of the container view. If size change, text layout will likely
   // change and should be updated.
   CGSize _previousSize;
 
   // Store values that were used last time the rects were drawn.
   CGPoint _scroll;
   CGFloat _zoom;
   CGFloat _offset;
 
-  __unsafe_unretained id<ContextualSearchHighlighterDelegate> _delegate;
+  __weak id<ContextualSearchHighlighterDelegate> _delegate;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame
                      delegate:
                          (id<ContextualSearchHighlighterDelegate>)delegate {
   self = [super initWithFrame:frame];
   if (self) {
     [self setUserInteractionEnabled:NO];
     [self setAutoresizingMask:UIViewAutoresizingFlexibleWidth |
                               UIViewAutoresizingFlexibleHeight];
@@ skipping 31 matching lines @@
     [view removeFromSuperview];
   }
   for (NSValue* value in rects) {
     CGRect rect = [value CGRectValue];
     rect.origin.x *= zoom;
     rect.origin.y *= zoom;
     rect.size.width *= zoom;
     rect.size.height *= zoom;
     rect.origin.x -= scroll.x;
     rect.origin.y += offset - scroll.y;
-    UIView* view = [[[UIView alloc] initWithFrame:rect] autorelease];
+    UIView* view = [[UIView alloc] initWithFrame:rect];
     [self addSubview:view];
     view.backgroundColor =
         [UIColor colorWithRed:0.67 green:0.88 blue:0.96 alpha:0.6];
   }
   [[self superview] bringSubviewToFront:self];
   _zoom = zoom;
   _scroll = scroll;
   _offset = offset;
 }
 
@@ skipping 20 matching lines @@
   CGRect bounding = CGRectNull;
   for (UIView* view : [self subviews]) {
     bounding = CGRectUnion(bounding, view.frame);
   }
   bounding.origin.x += _scroll.x;
   bounding.origin.y += _scroll.y;
   return bounding;
 }
 
 @end