dart2js: put all type-test related properties on the prototype and not on the constructor.

tests/corelib/safe_to_string_test.dart

Index: tests/corelib/safe_to_string_test.dart
diff --git a/tests/corelib/safe_to_string_test.dart b/tests/corelib/safe_to_string_test.dart
index c48b5dddc376b6fb4eb8e0a41549b22eec8680a2..ad2fbdc67941f6d33dcada2d8400174311acc44a 100644
--- a/tests/corelib/safe_to_string_test.dart
+++ b/tests/corelib/safe_to_string_test.dart
@@ -28,6 +28,8 @@ main() {
   Expect.stringEquals('null', Error.safeToString(null));
   Expect.stringEquals('true', Error.safeToString(true));
   Expect.stringEquals('false', Error.safeToString(false));
-  Expect.stringEquals("Instance of 'Object'",
+  // The class name may be minified.
+  String className = "$Object";
+  Expect.stringEquals("Instance of '$className'",
                       Error.safeToString(new Object()));
 }