Add two constructor tests

tests/language/src/Constructor3Test.dart

+// Copyright (c) 2011, 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.
+// Dart test program for constructors and initializers.
+
+// Expect the initializer expressions E(i) to be evaluated
+// in the order 1, 2, 3, ...
+// Each expression must be evaluated exactly once.
+
+String trace = "";
+
+int E(int i) {
+  trace += "$i-";
+  return i;
+}
+
+class A {
+  var a1;
+  A(x, y) : a1 = E(3) {
+    Expect.equals(1, x);
+    Expect.equals(2, y);
+    E(5);
+  }
+}
+
+class B extends A {
+  var b1;
+  B(x) : super(E(1), E(2)), b1 = E(4) {
+    // Implicit super call to A's body happens here.
+    Expect.equals(4, b1);
+    E(6);
+  }
+}
+
+main() {
+  var b = new B(0);
+  Expect.equals("1-2-3-4-5-6-", trace);
+}