Re-apply "What if you closurize identical?" but this time don't be magic: it requires the compiler …

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/lib/js_helper.dart	(revision 16786)
+++ sdk/lib/_internal/compiler/implementation/lib/js_helper.dart	(working copy)
@@ -821,6 +821,12 @@
     // TODO(ahe): How to safely access $?
     return JS('var', r'$[#]', className);
   }
+
+  static bool identical(a, b) {
+    return JS('bool', '# == null', a)
+      ? JS('bool', '# == null', b)
+      : JS('bool', '# === #', a, b);
+  }
 }
 
 /**