Introduce few const getters for dom classes

third_party/WebKit/Source/core/dom/DOMStringMap.h

 /*
  * Copyright (C) 2010 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 63 matching lines @@
     }
     bool anonymousIndexedSetter(uint32_t index, const String& value, ExceptionState& exceptionState)
     {
         return anonymousNamedSetter(String::number(index), value, exceptionState);
     }
     DeleteResult anonymousIndexedDeleter(uint32_t index)
     {
         return anonymousNamedDeleter(AtomicString::number(index));
     }
 
-    virtual Element* element() = 0;
+    virtual Element* element() const = 0;
 
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
 protected:
     DOMStringMap() { }
 };
 
 } // namespace blink
 
 #endif // DOMStringMap_h