Implement Custom Elements' attributeChangedCallback.

Source/core/dom/CustomElementLifecycleCallbacks.h

 /*
  * 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 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef CustomElementLifecycleCallbacks_h
 #define CustomElementLifecycleCallbacks_h
 
 #include "wtf/RefCounted.h"
+#include "wtf/text/AtomicString.h"
 
 namespace WebCore {
 
 class Element;
 
 class CustomElementLifecycleCallbacks : public RefCounted<CustomElementLifecycleCallbacks> {
 public:
     virtual ~CustomElementLifecycleCallbacks() { }
 
-    bool hasCreated() const { return m_which == Created; }
+    bool hasCreated() const { return m_which & Created; }
     virtual void created(Element*) = 0;
 
+    bool hasAttributeChanged() const { return m_which & AttributeChanged; }
+    virtual void attributeChanged(Element*, const AtomicString& name, const AtomicString& oldValue, const AtomicString& newValue) = 0;
+
     enum CallbackType {
-        None,
-        Created
+        None             = 0,
+        Created          = 1 << 0,
+        AttributeChanged = 1 << 1
     };
 
 protected:
     CustomElementLifecycleCallbacks(CallbackType which) : m_which(which) { }
 
 private:
     CallbackType m_which;
 };
 
 }
 
 #endif // CustomElementLifecycleCallbacks_h