Build HTMLFormElement::m_associatedElements lazily

Source/core/dom/IdTargetObserverRegistry.cpp

Index: Source/core/dom/IdTargetObserverRegistry.cpp
diff --git a/Source/core/dom/IdTargetObserverRegistry.cpp b/Source/core/dom/IdTargetObserverRegistry.cpp
index 19d297ad5e7d24be1f802fb74b6b45670db0c828..45ad4dc1a758096bfe12a44374f2e32a31f5beaf 100644
--- a/Source/core/dom/IdTargetObserverRegistry.cpp
+++ b/Source/core/dom/IdTargetObserverRegistry.cpp
@@ -82,4 +82,12 @@ void IdTargetObserverRegistry::notifyObserversInternal(const AtomicString& id)
     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