Implement modular compilation

test/samples/trusttypes2.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.
-
-class A {
-  int x = 42;
-}
-
-typedef int AA(A a);
-
-void bar(AA aa, a) {
-  // Is this integer addition?
-  print(aa(a) + aa(a));
-}
-
-void main() {
-  List<A> list = <A>[];
-  list.add(new A());
-  list.add(new B(new Point(1, 2)));
-  list.forEach((A a) => bar((a) => a.x, a));
-}
-
-class B extends A {
-  var _x;
-  B(this._x);
-
-  get x => _x;
-}
-
-class Point {
-  int x;
-  int y;
-  Point(this.x, this.y);
-  Point operator +(Point other) {
-    return new Point(this.x + other.x, this.y + other.y);
-  }
-  String toString() => "($x, $y)";
-}