Implement updated method overriding rules (issue 2943).

tests/language/method_override2_test.dart

+// Copyright (c) 2012, 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.
+
+// Checks that an overriding method has compatible parameters.
+
+interface I {
+  m([a, b]);
+}
+
+interface J extends I { }
+
+interface K extends J {
+  m([c, d]);  /// 00: compile-time error
+}
+
+class C implements I {
+  m([a, b]) {
+    print("$a $b");
+  }
+}
+
+class D
+    extends C  /// 01: compile-time error
+    implements I  /// 02: compile-time error
+    implements J  /// 03: compile-time error
+{
+  m([c, d]) {
+    print("$c $d");
+  }
+}
+
+
+int main() {
+  var c = new C();
+  c.m(a: "hello", b: "world");
+  var d = new D();
+  d.m(c: "hello", d: "world");
+  print("${c is I} ${d is I} ${d is I} ${d is J}");
+}
+