Add a const version of JSONObject::cast()

third_party/WebKit/Source/platform/json/JSONValues.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 159 matching lines @@
   static std::unique_ptr<JSONObject> create() {
     return WTF::wrapUnique(new JSONObject());
   }
 
   static JSONObject* cast(JSONValue* value) {
     if (!value || value->getType() != TypeObject)
       return nullptr;
     return static_cast<JSONObject*>(value);
   }
 
+  static const JSONObject* cast(const JSONValue* value) {
+    if (!value || value->getType() != TypeObject)
+      return nullptr;
+    return static_cast<const JSONObject*>(value);
+  }
+
   static std::unique_ptr<JSONObject> from(std::unique_ptr<JSONValue> value) {
     auto maybeObject = WTF::wrapUnique(JSONObject::cast(value.get()));
     if (maybeObject)
       value.release();
     return maybeObject;
   }
 
   static void cast(JSONObject*) = delete;
   static void cast(std::unique_ptr<JSONObject>) = delete;
 
@@ skipping 89 matching lines @@
   JSONArray();
   Vector<std::unique_ptr<JSONValue>> m_data;
 };
 
 PLATFORM_EXPORT void escapeStringForJSON(const String&, StringBuilder*);
 void doubleQuoteStringForJSON(const String&, StringBuilder*);
 
 }  // namespace blink
 
 #endif  // JSONValues_h