Implement implicit constructors in mixin applications.

tests/language/mixin_super_constructor_multiple_test.dart

Index: tests/language/mixin_super_constructor_multiple_test.dart
diff --git a/tests/language/return_this_type_test.dart b/tests/language/mixin_super_constructor_multiple_test.dart
similarity index 62%
copy from tests/language/return_this_type_test.dart
copy to tests/language/mixin_super_constructor_multiple_test.dart
index d7ad7396b75adadc6c933958ce131bae7354ddd5..9e40a249d2f91cededa1d70bbab6f5dfd6ca5510 100644
--- a/tests/language/return_this_type_test.dart
+++ b/tests/language/mixin_super_constructor_multiple_test.dart
@@ -2,17 +2,21 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// Make sure the engine does not infer the wrong type for [:A.foo:].
-
 import "package:expect/expect.dart";
 
-class A {
-  foo() => this;
+class S {
+  int i;
+  S.foo() : i = 1742;
 }
 
-class B extends A {
+class M1 { }
+
+class M2 { }
+
+class C extends S with M1, M2 {
+  C.foo() : super.foo();
 }
 
 main() {
-  Expect.isTrue(new B().foo() is B);
+  Expect.equals(1742, new C.foo().i);
 }