Bug 394442, Optimize ID, class and style getters, r=bz+sicking, sr=sicking, a=jst

content/base/src/nsGenericElement.cpp

@@ -2268,6 +2268,10 @@ nsGenericElement::DispatchDOMEvent(nsEvent* aEvent,
 nsIAtom*
 nsGenericElement::GetID() const
 {
+  if (!HasFlag(NODE_MAY_HAVE_ID)) {
+    return nsnull;
+  }
+
   nsIAtom* IDName = GetIDAttributeName();
   if (IDName) {
     const nsAttrValue* attrVal = mAttrsAndChildren.GetAttr(IDName);
@@ -3683,6 +3687,7 @@ nsGenericElement::ParseAttribute(PRInt32 aNamespaceID,
 {
   if (aNamespaceID == kNameSpaceID_None &&
       aAttribute == GetIDAttributeName() && !aValue.IsEmpty()) {
+    SetFlags(NODE_MAY_HAVE_ID);
     // Store id as an atom.  id="" means that the element has no id,
     // not that it has an emptystring as the id.
     aResult.ParseAtom(aValue);