Implement Custom Elements' entered and left document callbacks.

Source/core/dom/CustomElementLifecycleCallbacks.h

Index: Source/core/dom/CustomElementLifecycleCallbacks.h
diff --git a/Source/core/dom/CustomElementLifecycleCallbacks.h b/Source/core/dom/CustomElementLifecycleCallbacks.h
index 11838feeb5339ab186d53e1d1fc808d8e51fbfa2..011db7e1b12660553bfb79168732cc649da91b65 100644
--- a/Source/core/dom/CustomElementLifecycleCallbacks.h
+++ b/Source/core/dom/CustomElementLifecycleCallbacks.h
@@ -45,13 +45,21 @@ public:
     bool hasCreated() const { return m_which & Created; }
     virtual void created(Element*) = 0;
 
+    bool hasEnteredDocument() const { return m_which & EnteredDocument; }
+    virtual void enteredDocument(Element*) = 0;
+
+    bool hasLeftDocument() const { return m_which & LeftDocument; }
+    virtual void leftDocument(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             = 0,
         Created          = 1 << 0,
-        AttributeChanged = 1 << 1
+        EnteredDocument  = 1 << 1,
+        LeftDocument     = 1 << 2,
+        AttributeChanged = 1 << 3
     };
 
 protected: