DOMTokenList.contains() should not throw.

third_party/WebKit/Source/core/dom/DOMTokenList.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:
  * 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 49 matching lines @@
   return true;
 }
 
 // https://dom.spec.whatwg.org/#concept-domtokenlist-validation
 bool DOMTokenList::ValidateTokenValue(const AtomicString&,
                                       ExceptionState& exception_state) const {
   exception_state.ThrowTypeError("DOMTokenList has no supported tokens.");
   return false;
 }
 
-bool DOMTokenList::contains(const AtomicString& token,
-                            ExceptionState& exception_state) const {
-  if (!ValidateToken(token, exception_state))
-    return false;
+// https://dom.spec.whatwg.org/#dom-domtokenlist-contains
+bool DOMTokenList::contains(const AtomicString& token) const {
   return ContainsInternal(token);
 }
 
 void DOMTokenList::add(const AtomicString& token,
                        ExceptionState& exception_state) {
   Vector<String> tokens;
   tokens.push_back(token.GetString());
   add(tokens, exception_state);
 }
 
@@ skipping 190 matching lines @@
   return tokens_.Contains(token);
 }
 
 const AtomicString DOMTokenList::item(unsigned index) const {
   if (index >= length())
     return AtomicString();
   return tokens_[index];
 }
 
 }  // namespace blink