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

ios/chrome/browser/ui/contextual_search/window_gesture_observer.mm

 // 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.
 
 #include "ios/chrome/browser/ui/contextual_search/window_gesture_observer.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation WindowGestureObserver {
   NSObject* _target;
   SEL _action;
   BOOL _actionPassesSelf;
 }
 
 @synthesize viewToExclude = _viewToExclude;
 @synthesize touchedView = _touchedView;
 
 - (instancetype)initWithTarget:(id)target action:(SEL)action {
@@ skipping 18 matching lines @@
 - (void)addTarget:(id)target action:(SEL)action {
   // No-op.
 }
 
 - (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
   _touchedView = nil;
   for (UITouch* touch in touches) {
     if (![[touch view] isDescendantOfView:_viewToExclude]) {
       _touchedView = [touch view];
       dispatch_async(dispatch_get_main_queue(), ^{
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
         if (_actionPassesSelf) {
           [_target performSelector:_action withObject:self];
         } else {
           [_target performSelector:_action];
         }
+#pragma clang diagnostic pop
+
       });
       // Only invoke from the first qualifying touch.
       break;
     }
   }
 
   // Cancels to forward touch to other handlers.
   self.state = UIGestureRecognizerStateFailed;
   [super touchesBegan:touches withEvent:event];
 }
 
 @end