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

ios/chrome/browser/ui/stack_view/card_stack_pinch_gesture_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/chrome/browser/ui/stack_view/card_stack_pinch_gesture_recognizer.h"
 
 #include "base/logging.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface CardStackPinchGestureRecognizer ()
 
 // Returns the number of non-ended, non-cancelled touches in |event|.
 - (NSUInteger)numberOfActiveTouchesInEvent:(UIEvent*)event;
 
 @end
 
 @implementation CardStackPinchGestureRecognizer
 
 @synthesize numberOfActiveTouches = numberOfActiveTouches_;
@@ skipping 32 matching lines @@
   NSUInteger count = 0;
   for (UITouch* touch in [event touchesForGestureRecognizer:self]) {
     if (touch.phase == UITouchPhaseBegan || touch.phase == UITouchPhaseMoved ||
         touch.phase == UITouchPhaseStationary)
       count++;
   }
   return count;
 }
 
 @end