Introducing new API placeHolder() to expose placeholder attribute on MAC

Source/web/WebAXObject.cpp

 /*
  * 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 219 matching lines @@
 }
 
 WebString WebAXObject::ariaAutoComplete() const
 {
     if (isDetached())
         return WebString();
 
     return m_private->ariaAutoComplete();
 }
 
+WebString WebAXObject::placeholder() const
+{
+    if (isDetached())
+        return WebString();
+
+    return WebString(m_private->placeholder());
+}
+
 bool WebAXObject::isButtonStateMixed() const
 {
     if (isDetached())
         return false;
 
     return m_private->checkboxOrRadioValue() == ButtonStateMixed;
 }
 
 bool WebAXObject::isChecked() const
 {
@@ skipping 1013 matching lines @@
     m_private = object;
     return *this;
 }
 
 WebAXObject::operator WTF::PassRefPtr<AXObject>() const
 {
     return m_private.get();
 }
 
 } // namespace blink