Move toString() to collection classes.

tests/corelib/map_to_string_test.dart

Index: tests/corelib/map_to_string_test.dart
diff --git a/tests/compiler/dart2js_native/is_check_test.dart b/tests/corelib/map_to_string_test.dart
similarity index 65%
copy from tests/compiler/dart2js_native/is_check_test.dart
copy to tests/corelib/map_to_string_test.dart
index db045025b43c3a74fcc4bfe3f987650a3a66db7e..98b532f1749fb8c68691be29ba5a3645c698dc1e 100644
--- a/tests/compiler/dart2js_native/is_check_test.dart
+++ b/tests/corelib/map_to_string_test.dart
@@ -4,9 +4,12 @@
 
 import "package:expect/expect.dart";
 
-class A native "A" {}
-
-main() {
-  var a = [new Object()];
-  Expect.isFalse(a[0] is A);
-}
+void main() {
+  Map m = new Map();
+  
+  m[0] = 0;
+  m[1] = 1;
+  m[2] = m;
+  
+  Expect.equals('{0: 0, 1: 1, 2: {...}}', m.toString());
+}