Add use counter for the firefox extension containsNode()

Source/core/editing/Selection.idl

Index: Source/core/editing/Selection.idl
diff --git a/Source/core/editing/Selection.idl b/Source/core/editing/Selection.idl
index dc27b0d9bfbe2d06112f4fcaed18e339ecad9d87..c996a246591b3937eafc13ccea03b45ddfd57004 100644
--- a/Source/core/editing/Selection.idl
+++ b/Source/core/editing/Selection.idl
@@ -67,8 +67,7 @@
     // Firefox extensions
     // https://developer.mozilla.org/En/DOM/Selection
     //
-    // FIXME: Add use counters.
-    boolean containsNode([Default = Undefined] optional Node node, [Default = Undefined] optional boolean allowPartial);
+    [MeasureAs=SelectionContainsNode] boolean containsNode([Default = Undefined] optional Node node, [Default = Undefined] optional boolean allowPartial);
 
     // WebKit extensions
     [MeasureAs=SelectionBaseNode] readonly attribute Node baseNode;