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

ios/web/web_state/ui/crw_touch_tracking_recognizer.mm

 // Copyright 2012 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/web_state/ui/crw_touch_tracking_recognizer.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface CRWTouchTrackingRecognizer () <UIGestureRecognizerDelegate> {
-  id<CRWTouchTrackingDelegate> _delegate;  // weak
+  id<CRWTouchTrackingDelegate> __weak _delegate;
 }
 @end
 
 @implementation CRWTouchTrackingRecognizer
 
 @synthesize touchTrackingDelegate = _delegate;
 
 - (id)initWithDelegate:(id<CRWTouchTrackingDelegate>)delegate {
   if ((self = [super init])) {
     _delegate = delegate;
@@ skipping 32 matching lines @@
 #pragma mark -
 #pragma mark UIGestureRecognizerDelegate Method
 
 - (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer
     shouldRecognizeSimultaneouslyWithGestureRecognizer:
         (UIGestureRecognizer*)otherGestureRecognizer {
   return YES;
 }
 
 @end