[ios] Use new JS execution API in browsing data partitioning test.

ios/web/public/test/js_test_util.h

 // 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.
 
 #ifndef IOS_WEB_PUBLIC_TEST_JS_TEST_UTIL_H_
 #define IOS_WEB_PUBLIC_TEST_JS_TEST_UTIL_H_
 
 #import <Foundation/Foundation.h>
 #import <WebKit/WebKit.h>
 
 @class CRWJSInjectionManager;
 @class CRWJSInjectionReceiver;
 
 namespace web {
 
 // These functions synchronously execute JavaScript and return result as id.
 // id will be backed up by different classes depending on resulting JS type:
 // NSString (string), NSNumber (number or boolean), NSDictionary (object),
 // NSArray (array), NSNull (null), NSDate (Date), nil (undefined or execution
 // exception).
 
 // Executes JavaScript on the |manager| and returns the result as an id.
 id ExecuteJavaScript(CRWJSInjectionManager* manager, NSString* script);
 
 // Executes JavaScript on the |receiver| and returns the result as an id.
 id ExecuteJavaScript(CRWJSInjectionReceiver* receiver, NSString* script);
 
 // Executes JavaScript on |web_view| and returns the result as an id.
+// |error| can be null and will be updated only if script execution fails.
+id ExecuteJavaScript(WKWebView* web_view, NSString* script, NSError** error);
+
+// Executes JavaScript on |web_view| and returns the result as an id.
+// Fails if there was an error during script execution.
 id ExecuteJavaScript(WKWebView* web_view, NSString* script);
 
 }  // namespace web
 
 #endif  // IOS_WEB_PUBLIC_TEST_JS_TEST_UTIL_H_