DOMTokenList.contains() should not throw.

third_party/WebKit/Source/core/dom/DOMTokenList.cpp

Index: third_party/WebKit/Source/core/dom/DOMTokenList.cpp
diff --git a/third_party/WebKit/Source/core/dom/DOMTokenList.cpp b/third_party/WebKit/Source/core/dom/DOMTokenList.cpp
index e7d658e2a95146c7b8e8692f64b1320db8fa6b13..1446659eac750382785f954e679268238a4d7bc6 100644
--- a/third_party/WebKit/Source/core/dom/DOMTokenList.cpp
+++ b/third_party/WebKit/Source/core/dom/DOMTokenList.cpp
@@ -67,10 +67,8 @@ bool DOMTokenList::ValidateTokenValue(const AtomicString&,
   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);
 }