Implement Custom Elements' entered and left document callbacks.

Source/core/dom/CustomElementCallbackDispatcher.h

Index: Source/core/dom/CustomElementCallbackDispatcher.h
diff --git a/Source/core/dom/CustomElementCallbackDispatcher.h b/Source/core/dom/CustomElementCallbackDispatcher.h
index 915c96a8cee19b7449f33d86cef5c1d1b9eafc75..9b6f10d27c4a8b639bd850d16985b60ed83e453f 100644
--- a/Source/core/dom/CustomElementCallbackDispatcher.h
+++ b/Source/core/dom/CustomElementCallbackDispatcher.h
@@ -68,6 +68,8 @@ public:
 
     void enqueueAttributeChangedCallback(PassRefPtr<CustomElementLifecycleCallbacks>, PassRefPtr<Element>, const AtomicString& name, const AtomicString& oldValue, const AtomicString& newValue);
     void enqueueCreatedCallback(PassRefPtr<CustomElementLifecycleCallbacks>, PassRefPtr<Element>);
+    void enqueueEnteredDocumentCallback(PassRefPtr<CustomElementLifecycleCallbacks>, PassRefPtr<Element>);
+    void enqueueLeftDocumentCallback(PassRefPtr<CustomElementLifecycleCallbacks>, PassRefPtr<Element>);
 
     // Returns true if more work may have to be performed at the
     // checkpoint by this or other workers (for example, this work
@@ -103,8 +105,9 @@ private:
     static void processElementQueueAndPop();
     void processElementQueueAndPop(size_t start, size_t end);
 
-    CustomElementCallbackQueue* createCallbackQueue(PassRefPtr<CustomElementLifecycleCallbacks>, PassRefPtr<Element>);
-    CustomElementCallbackQueue* ensureCallbackQueue(PassRefPtr<CustomElementLifecycleCallbacks>, PassRefPtr<Element>);
+    CustomElementCallbackQueue* createCallbackQueue(PassRefPtr<Element>);
+    CustomElementCallbackQueue* ensureCallbackQueue(PassRefPtr<Element>);
+    CustomElementCallbackQueue* scheduleInCurrentElementQueue(PassRefPtr<Element>);
 
     // The processing stack, flattened. Element queues lower in the
     // stack appear toward the head of the vector. The first element