Start allowing mixin application extensions.

tests/language/mixin_naming_test.dart

Index: tests/language/mixin_naming_test.dart
diff --git a/tests/language/mixin_naming_test.dart b/tests/language/mixin_naming_test.dart
index 6aaa2acd17c5c57a9d2402de87671dcf93960155..b3b4a9c6bf85c6a93c9b1786963b2eb10b68287c 100644
--- a/tests/language/mixin_naming_test.dart
+++ b/tests/language/mixin_naming_test.dart
@@ -8,6 +8,7 @@ class M2 { }
 class M3 { }
 
 typedef C = S with M1, M2, M3;
+class D extends S with M1, M2, M3 { }
 
 class S_M1 { }
 class S_M1_M2 { }
@@ -15,18 +16,28 @@ class S_M1_M2 { }
 main() {
   var c = new C();
   Expect.isTrue(c is C);
+  Expect.isFalse(c is D);
   Expect.isTrue(c is S);
   Expect.isFalse(c is S_M1);
   Expect.isFalse(c is S_M1_M2);
 
+  var d = new D();
+  Expect.isFalse(d is C);
+  Expect.isTrue(d is D);
+  Expect.isTrue(d is S);
+  Expect.isFalse(d is S_M1);
+  Expect.isFalse(d is S_M1_M2);
+
   var sm = new S_M1();
   Expect.isFalse(sm is C);
+  Expect.isFalse(sm is D);
   Expect.isFalse(sm is S);
   Expect.isTrue(sm is S_M1);
   Expect.isFalse(sm is S_M1_M2);
 
   var smm = new S_M1_M2();
   Expect.isFalse(smm is C);
+  Expect.isFalse(smm is D);
   Expect.isFalse(smm is S);
   Expect.isFalse(smm is S_M1);
   Expect.isTrue(smm is S_M1_M2);