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

tests/language/generic_object_type_test.dart

Index: tests/language/generic_object_type_test.dart
diff --git a/tests/language/rewrite_assign_test.dart b/tests/language/generic_object_type_test.dart
similarity index 56%
copy from tests/language/rewrite_assign_test.dart
copy to tests/language/generic_object_type_test.dart
index 5379a6ca35bf171a8d2f276529597b1355e26a57..4b1733a63a3eb4240d5b26b17257629968b0b548 100644
--- a/tests/language/rewrite_assign_test.dart
+++ b/tests/language/generic_object_type_test.dart
@@ -4,23 +4,13 @@
 
 import "package:expect/expect.dart";
 
-bar(x,y) {}
-
-foo(b) {
-  var x, y;
-  if (b) {
-    x = 1;
-    y = 2;
-  } else {
-    x = 2;
-    y = 1;
+class Tester<T> {
+  testGenericType(x) {
+    return x is T;
   }
-  bar(x,y);
-  bar(x,y);
-  return x;
 }
 
 main() {
-    Expect.equals(1, foo(true));
-    Expect.equals(2, foo(false));
+  // The Dart Object type is special in that it doesn't have any superclass.
+  Expect.isTrue(new Tester<Object>().testGenericType(new Object()));
 }