Add --package-root option to the compiler.

dart/tests/utils/dummy_compiler_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.
 
 // Smoke test of the dart2js compiler API.
 
 #import('../../lib/compiler/compiler.dart');
 #import('dart:uri');
 
 Future<String> provider(Uri uri) {
@@ skipping 27 matching lines @@
   }
   completer.complete(source);
   return completer.future;
 }
 
 void handler(Uri uri, int begin, int end, String message, bool fatal) {
   print(message);
 }
 
 main() {
-  String code = compile(new Uri(scheme: 'main'), new Uri(scheme: 'lib'),
+  String code = compile(new Uri(scheme: 'main'),
+                        new Uri(scheme: 'lib'),
+                        new Uri(scheme: 'package'),
                         provider, handler).value;
   if (code === null) {
     throw 'Compilation failed';
   }
 }