Handle generic parameters in synthesized constructor for mixin applications.

tests/language/generic_constructor_mixin3_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 C1 = A<int> with B;
+class C2 = A<String> with B;
+
+void main() {
+  var v = 0;
+  checkNoDynamicTypeError(() => new C1(v));
+  checkDynamicTypeError(() => new C2(v));
+}