Better handling of DocumentOrderedMap same-ID lookups during tree removals

third_party/WebKit/Source/core/dom/TreeScope.cpp

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 168 matching lines @@
 }
 
 void TreeScope::addElementById(const AtomicString& elementId, Element* element)
 {
     if (!m_elementsById)
         m_elementsById = DocumentOrderedMap::create();
     m_elementsById->add(elementId, element);
     m_idTargetObserverRegistry->notifyObservers(elementId);
 }
 
+
+#if ENABLE(ASSERT)
+namespace {
+
+class RemovingElementIdScope {
+    STACK_ALLOCATED();
+public:
+    RemovingElementIdScope(DocumentOrderedMap& elementsById, const AtomicString& id)
+        : m_elementsById(&elementsById)
+    {
+        m_elementsById->willRemoveId(id);
+    }
+    ~RemovingElementIdScope()
+    {
+        m_elementsById->willRemoveId(nullAtom);
+    }
+
+private:
+    RawPtrWillBeMember<DocumentOrderedMap> m_elementsById;
+};
+
+}
+#endif
+
 void TreeScope::removeElementById(const AtomicString& elementId, Element* element)
 {
     if (!m_elementsById)
         return;
     m_elementsById->remove(elementId, element);
+#if ENABLE(ASSERT)
+    // Register 'elementId' as being removed. This is done should observers
+    // attempt to also look it up, something that the underlying DocumentOrderedMap
+    // is incapable of answering precisely while an element (and its
+    // children) are being removed from the tree. This is _only_ done to avoid
+    // an assert in DocumentOrderedMap::get() from falsely triggering for such
+    // unusual and unexpected lookups.
+    RemovingElementIdScope removalScope(*m_elementsById, elementId);
+#endif
     m_idTargetObserverRegistry->notifyObservers(elementId);
 }
 
 Node* TreeScope::ancestorInThisScope(Node* node) const
 {
     while (node) {
         if (node->treeScope() == this)
             return node;
         if (!node->isInShadowTree())
             return 0;
@@ skipping 370 matching lines @@
     visitor->trace(m_parentTreeScope);
     visitor->trace(m_idTargetObserverRegistry);
     visitor->trace(m_selection);
     visitor->trace(m_elementsById);
     visitor->trace(m_imageMapsByName);
     visitor->trace(m_labelsByForAttribute);
     visitor->trace(m_scopedStyleResolver);
 }
 
 } // namespace blink