Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/public/cwv_user_content_controller.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_USER_CONTENT_CONTROLLER_H_
+#define IOS_WEB_VIEW_PUBLIC_CWV_USER_CONTENT_CONTROLLER_H_
+
+#import <Foundation/Foundation.h>
+
+@class CWVUserScript;
+
+// Allows injecting custom scripts into CWVWebView created with the
+// configuration.
+@interface CWVUserContentController : NSObject
+
+// The user scripts associated with the configuration.
+@property(nonatomic, copy, readonly, nonnull)
+    NSArray<CWVUserScript*>* userScripts;
+
+- (nonnull instancetype)init NS_UNAVAILABLE;
+
+// Adds a user script.
+- (void)addUserScript:(nonnull CWVUserScript*)userScript;
+
+// Removes all associated user scripts.
+- (void)removeAllUserScripts;
+
+@end
+
+#endif  // IOS_WEB_VIEW_PUBLIC_CWV_USER_CONTENT_CONTROLLER_H_