Implement :valid and :invalid pseudoclass for <form>

Source/core/html/HTMLFormElement.h

Index: Source/core/html/HTMLFormElement.h
diff --git a/Source/core/html/HTMLFormElement.h b/Source/core/html/HTMLFormElement.h
index 1772b640e8a19b13adb32930fb9b37439e6321b9..5ddf24f8d75053a3b9fba81caa4564923a673041 100644
--- a/Source/core/html/HTMLFormElement.h
+++ b/Source/core/html/HTMLFormElement.h
@@ -53,6 +53,9 @@ public:
     virtual ~HTMLFormElement();
     virtual void trace(Visitor*) OVERRIDE;
 
+    virtual bool willValidate() const OVERRIDE FINAL;
+    virtual bool isValidElement() OVERRIDE FINAL;
+
     PassRefPtrWillBeRawPtr<HTMLFormControlsCollection> elements();
     void getNamedElements(const AtomicString&, WillBeHeapVector<RefPtrWillBeMember<Element> >&);