Mark the AtomicString(const String&) constructor as explicit

Source/core/loader/FormSubmission.cpp

 /*
  * Copyright (C) 2010 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 157 matching lines @@
             if (node->isElementNode() && toElement(node)->isFormControlElement()) {
                 submitButton = toHTMLFormControlElement(node);
                 break;
             }
         }
     }
 
     FormSubmission::Attributes copiedAttributes;
     copiedAttributes.copyFrom(attributes);
     if (submitButton) {
-        String attributeValue;
+        AtomicString attributeValue;
         if (!(attributeValue = submitButton->fastGetAttribute(formactionAttr)).isNull())
             copiedAttributes.parseAction(attributeValue);
         if (!(attributeValue = submitButton->fastGetAttribute(formenctypeAttr)).isNull())
             copiedAttributes.updateEncodingType(attributeValue);
         if (!(attributeValue = submitButton->fastGetAttribute(formmethodAttr)).isNull())
             copiedAttributes.updateMethodType(attributeValue);
         if (!(attributeValue = submitButton->fastGetAttribute(formtargetAttr)).isNull())
             copiedAttributes.setTarget(attributeValue);
     }
 
@@ skipping 81 matching lines @@
             frameRequest.resourceRequest().setHTTPContentType(m_contentType);
         else
             frameRequest.resourceRequest().setHTTPContentType(m_contentType + "; boundary=" + m_boundary);
     }
 
     frameRequest.resourceRequest().setURL(requestURL());
     FrameLoader::addHTTPOriginIfNeeded(frameRequest.resourceRequest(), AtomicString(m_origin));
 }
 
 }