Build HTMLFormElement::m_associatedElements lazily

Source/core/dom/IdTargetObserverRegistry.cpp

 /*
  * Copyright (C) 2012 Google 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 64 matching lines @@
         if (m_notifyingObserversInSet->contains(*it))
             (*it)->idTargetChanged();
     }
 
     if (m_notifyingObserversInSet->isEmpty())
         m_registry.remove(id.impl());
 
     m_notifyingObserversInSet = 0;
 }
 
+bool IdTargetObserverRegistry::hasObservers(const AtomicString& id) const
+{
+    if (id.isEmpty() || m_registry.isEmpty())
+        return false;
+    ObserverSet* set = m_registry.get(id.impl());
+    return set && !set->isEmpty();
+}
+
 } // namespace WebCore