Issue #2678 - Make QIing to a few often-used CCed classes faster.

QIing to CC interfaces is a hot path for a few widely-used classes.
Presumably there are many of these objects being created and destroyed.
By making these classes check first for the CC interfaces directly, rather
than going up the inheritance chain, the resulting overhead is reduced.

dom/base/nsTextNode.cpp

@@ -97,8 +97,13 @@ nsTextNode::~nsTextNode()
 {
 }
 
-NS_IMPL_ISUPPORTS_INHERITED(nsTextNode, nsGenericDOMDataNode, nsIDOMNode,
-                            nsIDOMText, nsIDOMCharacterData)
+// Using the CC variant of this, even though this class does not define
+// a new CC participant, to make QIing to the CC interfaces faster.
+NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED(nsTextNode,
+                                             nsGenericDOMDataNode,
+                                             nsIDOMNode,
+                                             nsIDOMText,
+                                             nsIDOMCharacterData)
 
 JSObject*
 nsTextNode::WrapNode(JSContext *aCx, JS::Handle<JSObject*> aGivenProto)