Handle generic parameters in synthesized constructor for mixin applications.

tests/language/generic_constructor_mixin2_test.dart

+// Copyright (c) 2014, 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.
+
+// Test that parameter types types are checked correctly in the face of
+// mixin application upon a generic constructor.
+
+import 'checked_mode_helper.dart';
+
+class A<X> {
+  A(X x);
+}
+
+class B {}
+class C {}
+
+class D<Y> = A<Y> with B, C;
+
+void main() {
+  var v = 0;
+  checkNoDynamicTypeError(() => new D<int>(v));
+  checkDynamicTypeError(() => new D<String>(v));
+}