Collect is checks to only emit the ones that are needed.

frog/leg/compiler.dart

Index: frog/leg/compiler.dart
===================================================================
--- frog/leg/compiler.dart	(revision 5280)
+++ frog/leg/compiler.dart	(working copy)
@@ -361,6 +361,11 @@
     universe.instantiatedClasses.add(element);
   }
 
+  // TODO(ngeoffray): This should get a type.
+  void registerIsCheck(Element element) {
+    universe.isChecks.add(element);
+  }
+
   Type resolveType(ClassElement element) {
     return withCurrentElement(element, () => resolver.resolveType(element));
   }