Change how runtime type information is being set in the backend.

lib/compiler/implementation/lib/js_helper.dart

Index: lib/compiler/implementation/lib/js_helper.dart
===================================================================
--- lib/compiler/implementation/lib/js_helper.dart	(revision 11430)
+++ lib/compiler/implementation/lib/js_helper.dart	(working copy)
@@ -960,7 +960,10 @@
 
 getRuntimeTypeInfo(target) {
   if (target === null) return null;
-  return JS('var', @'#.builtin$typeInfo', target);
+  var res = JS('var', @'#.builtin$typeInfo', target);
+  // If the object does not have runtime type information, return an
+  // empty literal, to avoid null checks.
+  return res == null ? JS('var', '{}') : res;

[kasperl, 2012/08/28 09:14:15]

I'd prefer () around the comparison. Would it be possible to re-use the object
returned in the case res is null? Seems wasteful to allocate a new object every
single time.

[ngeoffray, 2012/08/28 10:39:45]

I added a TODO to do that once we have lazy static initializations.

 }
 
 /**