Make JSONArray::at() a const member function.

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 24 matching lines @@
 #include "wtf/Allocator.h"
 #include "wtf/Forward.h"
 #include "wtf/HashMap.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/TypeTraits.h"
 #include "wtf/Vector.h"
 #include "wtf/text/StringHash.h"
 #include "wtf/text/WTFString.h"
 
 #include <memory>
+#include <utility>
 
 namespace blink {
 
 class JSONValue;
 
 }  // namespace blink
 
 namespace blink {
 
 class JSONArray;
@@ skipping 207 matching lines @@
   std::unique_ptr<JSONValue> clone() const override;
 
   void pushBoolean(bool);
   void pushInteger(int);
   void pushDouble(double);
   void pushString(const String&);
   void pushValue(std::unique_ptr<JSONValue>);
   void pushObject(std::unique_ptr<JSONObject>);
   void pushArray(std::unique_ptr<JSONArray>);
 
-  JSONValue* at(size_t index);
+  JSONValue* at(size_t index) const;
   size_t size() const { return m_data.size(); }
 
  protected:
   void prettyWriteJSONInternal(StringBuilder* output, int depth) const override;
 
  private:
   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