Handle some failing DocumentOrderedMap ID lookups across tree removals.

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

 /*
  * 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 125 matching lines @@
     TreeScope* commonAncestorTreeScope(TreeScope& other);
 
     Element* getElementByAccessKey(const String& key) const;
 
     DECLARE_VIRTUAL_TRACE();
 
     ScopedStyleResolver* scopedStyleResolver() const { return m_scopedStyleResolver.get(); }
     ScopedStyleResolver& ensureScopedStyleResolver();
     void clearScopedStyleResolver();
 
+#if ENABLE(ASSERT)
+    class RemoveScope {
+        STACK_ALLOCATED();
+    public:
+        explicit RemoveScope(ContainerNode*);

[esprehn, 2016/01/05 07:48:33]

reference, this should also be nested inside the map, not in the TreeScope.

+        ~RemoveScope();
+    private:
+        RawPtrWillBeMember<DocumentOrderedMap> m_idMap;
+    };
+#endif
+
 protected:
     TreeScope(ContainerNode&, Document&);
     TreeScope(Document&);
     virtual ~TreeScope();
 
 #if !ENABLE(OILPAN)
     void destroyTreeScopeData();
 #endif
 
     void setDocument(Document& document) { m_document = &document; }
     void setParentTreeScope(TreeScope&);
 
 #if !ENABLE(OILPAN)
     bool hasGuardRefCount() const { return m_guardRefCount; }
 #endif
 
     void setNeedsStyleRecalcForViewportUnits();
 
 private:
+    friend class RemoveScope;
+
 #if !ENABLE(OILPAN)
     virtual void dispose() { }
 
     int refCount() const;
 
 #if ENABLE(SECURITY_ASSERT)
     bool deletionHasBegun();
     void beginDeletion();
 #else
     bool deletionHasBegun() { return false; }
@@ skipping 33 matching lines @@
     return m_elementsById && m_elementsById->containsMultiple(id);
 }
 
 DEFINE_COMPARISON_OPERATORS_WITH_REFERENCES(TreeScope)
 
 HitTestResult hitTestInDocument(const Document*, int x, int y, const HitTestRequest& = HitTestRequest::ReadOnly | HitTestRequest::Active);
 
 } // namespace blink
 
 #endif // TreeScope_h