[ObjC ARC] Converts ios/chrome/browser/find_in_page:unit_tests_nonarc to ARC.

ios/chrome/browser/find_in_page/js_findinpage_manager_unittest.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.
 
 #import "ios/chrome/browser/find_in_page/js_findinpage_manager.h"
 
 #import <Foundation/Foundation.h>
 
 #import "base/test/ios/wait_util.h"
 #import "ios/chrome/browser/web/chrome_web_test.h"
 #import "ios/web/public/web_state/js/crw_js_injection_receiver.h"
 #import "ios/web/public/web_state/web_state.h"
 #import "testing/gtest_mac.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 // Test fixture to test Find In Page JS.
 class JsFindinpageManagerTest : public ChromeWebTest {
  protected:
   // Loads the given HTML and initializes the findInPage JS scripts.
   void LoadHtml(NSString* html) {
     ChromeWebTest::LoadHtml(html);
     manager_ =
         static_cast<JsFindinpageManager*>([web_state()->GetJSInjectionReceiver()
             instanceOfClass:[JsFindinpageManager class]]);
     [manager_ inject];
@@ skipping 46 matching lines @@
                 EXPECT_NSNE(@YES, result);
                 completion_handler_block_was_called = YES;
               }];
   };
   [manager_ findString:@"');token=true;('"
       completionHandler:completion_handler_block];
   base::test::ios::WaitUntilCondition(^bool() {
     return completion_handler_block_was_called;
   });
 }