Introduce the TYPEDEF element, and use it in order to catch passing closures to the DOM. I make the…

frog/leg/ssa/builder.dart

Index: frog/leg/ssa/builder.dart
===================================================================
--- frog/leg/ssa/builder.dart	(revision 5070)
+++ frog/leg/ssa/builder.dart	(working copy)
@@ -94,6 +94,10 @@
     return compiler.findHelper(const SourceString('unwrapException'));
   }
 
+  Element getClosureConverter() {
+    return compiler.findHelper(const SourceString('convertDartClosureToJS'));
+  }
+
   Element getTraceFromException() {
     return compiler.findHelper(const SourceString('getTraceFromException'));
   }