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

ios/chrome/browser/ui/contextual_search/touch_to_search_permissions_mediator+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/contextual_search/touch_to_search_permissions_mediator+testing.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace ios {
 class ChromeBrowserState;
 }
 
 static BOOL isTouchToSearchAvailable = YES;
 
 @implementation MockTouchToSearchPermissionsMediator
 @synthesize canSendPageURLs;
 @synthesize canPreloadSearchResults;
 @synthesize areContextualSearchQueriesSupported;
@@ skipping 27 matching lines @@
 
 - (void)setUpBrowserState:(ios::ChromeBrowserState*)browserState {
   // no-op, overriding superclass method.
 }
 
 - (BOOL)canExtractTapContextForURL:(const GURL&)url {
   return canExtractTapContextForAllURLs;
 }
 
 @end