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

ios/chrome/browser/ui/browser_view_controller_testing.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/browser_view_controller_testing.h"
 
 #import "ios/chrome/browser/ui/toolbar/web_toolbar_controller.h"
 #import "ios/chrome/browser/ui/toolbar/web_toolbar_controller_private.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface BrowserViewController (Private)
 
 - (WebToolbarController*)toolbarController;
 
 @end
 
 @implementation BrowserViewController (TestingAdditions)
 
 - (BOOL)testing_isLoading {
   return [[self toolbarController] isLoading];
 }
 
 - (void)testing_focusOmnibox {
   [[self toolbarController] focusOmnibox];
 }
 
 - (CGRect)testing_shareButtonAnchorRect {
   return [[self toolbarController] shareButtonAnchorRect];
 }
 
 @end