Add CWVUserContentController which enables injecting JavaScripts.

ios/web_view/internal/cwv_user_content_controller_internal.h

Index: ios/web_view/internal/cwv_user_content_controller_internal.h
diff --git a/ios/web_view/internal/cwv_user_content_controller_internal.h b/ios/web_view/internal/cwv_user_content_controller_internal.h
new file mode 100644
index 0000000000000000000000000000000000000000..37f6a7a239ffd14685a9c73ef7393a7085dd5bde
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+++ b/ios/web_view/internal/cwv_user_content_controller_internal.h
@@ -0,0 +1,19 @@
+// 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_INTERNAL_CWV_USER_CONTENT_CONTROLLER_INTERNAL_H_
+#define IOS_WEB_VIEW_INTERNAL_CWV_USER_CONTENT_CONTROLLER_INTERNAL_H_
+
+#import "ios/web_view/public/cwv_user_content_controller.h"
+
+@class CWVWebViewConfiguration;
+
+@interface CWVUserContentController ()
+
+- (nullable instancetype)initWithConfiguration:
+    (nonnull __weak CWVWebViewConfiguration*)configuration;
+
+@end
+
+#endif  // IOS_WEB_VIEW_INTERNAL_CWV_USER_CONTENT_CONTROLLER_INTERNAL_H_