Simplify inDetach() assert and make it stronger.

Source/core/dom/Node.cpp

Index: Source/core/dom/Node.cpp
diff --git a/Source/core/dom/Node.cpp b/Source/core/dom/Node.cpp
index 84963b9521a0c1034a43e6ef82b92498e61d62b8..fe8bea14b96edab82f97e0c2fa1831ae165b0c19 100644
--- a/Source/core/dom/Node.cpp
+++ b/Source/core/dom/Node.cpp
@@ -931,39 +931,17 @@ void Node::attach(const AttachContext&)
         cache->updateCacheAfterNodeIsAttached(this);
 }
 
-#if ENABLE(ASSERT)
-static Node* detachingNode;
-
-bool Node::inDetach() const
-{
-    return detachingNode == this;
-}
-#endif
-
 void Node::detach(const AttachContext& context)
 {
     ASSERT(document().lifecycle().stateAllowsDetach());
     DocumentLifecycle::DetachScope willDetach(document().lifecycle());
 
-#if ENABLE(ASSERT)
-    // The detaching might trigger destruction of a popup menu window,
-    // with ensuing detachment of its Nodes. In a separate document, so
-    // don't assert for these, but do set detachingNode to the most recent
-    // Node being detached.
-    ASSERT(!detachingNode || detachingNode->document() != document());
-    detachingNode = this;
-#endif
-
     if (layoutObject())
         layoutObject()->destroyAndCleanupAnonymousWrappers();
     setLayoutObject(nullptr);
 
     setStyleChange(NeedsReattachStyleChange);
     clearChildNeedsStyleInvalidation();
-
-#if ENABLE(ASSERT)
-    detachingNode = nullptr;
-#endif
 }
 
 void Node::reattachWhitespaceSiblingsIfNeeded(Text* start)