Allow super calls in mixins (for now behind a --supermixin flag).

tests/language/mixin_super_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// 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.
+// VMOptions=--supermixin
+
+import "package:expect/expect.dart";
+
+class MS<T> {
+  foo() {
+    return "MS<$T>.foo\n";
+  }
+}
+
+class M<T> extends MS<List<T>> {
+  foo() {
+    return super.foo() + "M<$T>.foo\n";
+  }
+}
+
+class NS<T> {
+  foo() {
+    return "NS<$T>.foo\n";
+  }
+}
+
+class N<T> extends NS<List<T>> {
+  foo() {
+    return super.foo() + "N<$T>.foo\n";
+  }
+}
+
+class S<T> {
+  foo() {
+    return "S<$T>.foo\n";
+  }
+}
+
+class SM<U, V> = S<List<U>> with M<Map<U, V>>;
+
+class MNA1<U, V, W> extends S<List<U>> with M<Map<U, V>>, N<W> {
+  foo() {
+    return super.foo() + "MNA1<$U, $V, $W>.foo\n";
+  }
+}
+
+class MNA2<U, V, W> extends SM<U, V> with N<W> {
+  foo() {
+    return super.foo() + "MNA2<$U, $V, $W>.foo\n";
+  }
+}
+
+class MNA3<U, V, W> extends S<List<U>> with SM<U, V>, N<W> {
+  foo() {
+    return super.foo() + "MNA3<$U, $V, $W>.foo\n";
+  }
+}
+
+main(){
+  Expect.equals("MS<List<double>>.foo\n"
+                "M<double>.foo\n",
+                new M<double>().foo());
+  Expect.equals("S<List<int>>.foo\n"
+                "M<Map<int, String>>.foo\n",
+                new SM<int, String>().foo());
+  Expect.equals("S<List<int>>.foo\n"
+                "M<Map<int, String>>.foo\n"
+                "N<bool>.foo\n"
+                "MNA1<int, String, bool>.foo\n",
+                new MNA1<int, String, bool>().foo());
+  Expect.equals("S<List<int>>.foo\n"
+                "M<Map<int, String>>.foo\n"
+                "N<bool>.foo\n"
+                "MNA2<int, String, bool>.foo\n",
+                new MNA2<int, String, bool>().foo());
+  Expect.equals("S<List<int>>.foo\n"
+                "M<Map<int, String>>.foo\n"
+                "N<bool>.foo\n"
+                "MNA3<int, String, bool>.foo\n",
+                new MNA3<int, String, bool>().foo());
+}
+