Gracefully handle a disconnected popup menu client on disposing open popup.

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 04356d0b344fbfe5426e8b81ea019cbf6708687a..4241f1be6d9ff812ee667b4108410dfc1ffae571 100644
--- a/Source/core/dom/Node.cpp
+++ b/Source/core/dom/Node.cpp
@@ -919,7 +919,11 @@ void Node::detach(const AttachContext& context)
     DocumentLifecycle::DetachScope willDetach(document().lifecycle());
 
 #if ENABLE(ASSERT)
-    ASSERT(!detachingNode);
+    // 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