Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/public/cwv_web_view_configuration.h

 // Copyright 2017 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_VIEW_PUBLIC_CWV_WEB_VIEW_CONFIGURATION_H_
 #define IOS_WEB_VIEW_PUBLIC_CWV_WEB_VIEW_CONFIGURATION_H_
 
 #import <Foundation/Foundation.h>
 
+@class CWVUserContentController;
 @class CWVWebsiteDataStore;
 
 // Configuration used for creation of a CWVWebView.
 @interface CWVWebViewConfiguration : NSObject<NSCopying>
 
 // Configuration with persistent data store which stores all data on disk.
 + (instancetype)defaultConfiguration;
 
 // Configuration with ephemeral data store that neven stores data on disk.
 + (instancetype)incognitoConfiguration;
 
 - (instancetype)init NS_UNAVAILABLE;
 
+// The user content controller to associate with web views created using this
+// configuration.
+@property(nonatomic, readonly) CWVUserContentController* userContentController;
+
 // YES if it is a configuration with persistent data store which stores all data
 // on disk.
-@property(readonly, getter=isPersistent) BOOL persistent;
+@property(nonatomic, readonly, getter=isPersistent) BOOL persistent;
 
 @end
 
 #endif  // IOS_WEB_VIEW_PUBLIC_CWV_WEB_VIEW_CONFIGURATION_H_