Handle platform access through prefix in dart2dart

tests/language/regress_21998_1_test.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
+import 'dart:math' as Math;
 import 'package:expect/expect.dart';
 
-import 'dart:_js_helper' show Primitives;
+main() {
+  Expect.equals(4, new C().m());
+}
 
-main() {
-  Expect.isFalse(Primitives.isD8);
-  Expect.isTrue(Primitives.isJsshell);
-}
+class C {
+  max(a) => a;
+
+  m() {
+    return max(Math.max(2, 4));
+  }
+}