Give more meaningful name to m_which in CustomElementLifecycleCallbacks

Source/core/dom/custom/CustomElementLifecycleCallbacks.h

Index: Source/core/dom/custom/CustomElementLifecycleCallbacks.h
diff --git a/Source/core/dom/custom/CustomElementLifecycleCallbacks.h b/Source/core/dom/custom/CustomElementLifecycleCallbacks.h
index 5f2b212010f41f74adfc3d918002d4c4de74c542..4e1302cbdfe3875feed7b97ccab1947675cc216d 100644
--- a/Source/core/dom/custom/CustomElementLifecycleCallbacks.h
+++ b/Source/core/dom/custom/CustomElementLifecycleCallbacks.h
@@ -50,7 +50,7 @@ public:
         AttributeChangedCallback = 1 << 3
     };
 
-    bool hasCallback(CallbackType type) const { return m_which & type; }
+    bool hasCallback(CallbackType type) const { return m_callbackType & type; }
 
     virtual void created(Element*) = 0;
     virtual void attached(Element*) = 0;
@@ -58,10 +58,10 @@ public:
     virtual void attributeChanged(Element*, const AtomicString& name, const AtomicString& oldValue, const AtomicString& newValue) = 0;
 
 protected:
-    CustomElementLifecycleCallbacks(CallbackType which) : m_which(which) { }
+    CustomElementLifecycleCallbacks(CallbackType type) : m_callbackType(type) { }
 
 private:
-    CallbackType m_which;
+    CallbackType m_callbackType;
 };
 
 }