Make atob() throw an InvalidCharacterError on excess padding characters

Source/core/page/DOMWindowBase64.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2013 Samsung Electronics. 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
@@ skipping 45 matching lines @@
 {
     if (encodedString.isNull())
         return String();
 
     if (!encodedString.containsOnlyLatin1()) {
         ec = InvalidCharacterError;
         return String();
     }
 
     Vector<char> out;
-    if (!base64Decode(encodedString, out, Base64FailOnInvalidCharacter)) {
+    if (!base64Decode(encodedString, out, Base64FailOnInvalidCharacter, Base64StrictPaddingValidation)) {
         ec = InvalidCharacterError;
         return String();
     }
 
     return String(out.data(), out.size());
 }
 
 } // namespace DOMWindowBase64
 
 } // namespace WebCore