Properly handle cascades in top-level functions

tests/language/cascade_in_expression_function_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.
 // Dart test program for testing throw statement
 
+makeMap() => new Map()..[3] = 4 ..[0] = 11;
+
 class MyClass {
   foo() => this..bar(3)..baz(4);
   bar(x) => x;
   baz(y) => y*2;
 }
 
 main() {
   var o = new MyClass();
   Expect.equals(o.foo(), o);
+  var g = makeMap();
+  Expect.equals(g[3], 4);
+  Expect.equals(g[0], 11);
 }