Use IDL argument default values in modules/encoding/

Source/modules/encoding/TextDecoder.cpp

 /*
  * Copyright (C) 2013 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 23 matching lines @@
 
 #include "bindings/v8/ExceptionState.h"
 #include "core/dom/ExceptionCode.h"
 #include "wtf/StringExtras.h"
 #include "wtf/text/TextEncodingRegistry.h"
 
 namespace WebCore {
 
 TextDecoder* TextDecoder::create(const String& label, const Dictionary& options, ExceptionState& exceptionState)
 {
-    const String& encodingLabel = label.isNull() ? String("utf-8") : label;
-
-    WTF::TextEncoding encoding(encodingLabel);
+    WTF::TextEncoding encoding(label);
     // The replacement encoding is not valid, but the Encoding API also
     // rejects aliases of the replacement encoding.
     if (!encoding.isValid() || !strcasecmp(encoding.name(), "replacement")) {
-        exceptionState.throwTypeError("The encoding label provided ('" + encodingLabel + "') is invalid.");
+        exceptionState.throwTypeError("The encoding label provided ('" + label + "') is invalid.");
         return 0;
     }
 
     bool fatal = false;
     options.get("fatal", fatal);
 
     bool ignoreBOM = false;
     options.get("ignoreBOM", ignoreBOM);
 
     return new TextDecoder(encoding, fatal, ignoreBOM);
@@ skipping 48 matching lines @@
             s.remove(0);
     }
 
     if (flush)
         m_bomSeen = false;
 
     return s;
 }
 
 } // namespace WebCore