- Fix more bad uses of Platform.packageRoot.

tests/compiler/dart2js/memory_compiler.dart

 // Copyright (c) 2013, 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.
 
 library dart2js.test.memory_compiler;
 
 import 'dart:async';
 
 import 'package:compiler/compiler.dart' show
     DiagnosticHandler;
@@ skipping 247 matching lines @@
     handler = (Uri uri, int begin, int end, String message, Diagnostic kind) {};
   }
   return handler;
 }
 
 Future<MirrorSystem> mirrorSystemFor(Map<String,String> memorySourceFiles,
                                      {DiagnosticHandler diagnosticHandler,
                                       List<String> options: const [],
                                       bool showDiagnostics: true}) {
   Uri libraryRoot = Uri.base.resolve('sdk/');
-  Uri packageRoot = Uri.base.resolveUri(
-      new Uri.file('${Platform.packageRoot}/'));
+  Uri packageRoot = Uri.base.resolve(Platform.packageRoot);
 
   var provider = new MemorySourceFileProvider(memorySourceFiles);
   var handler =
       createDiagnosticHandler(diagnosticHandler, provider, showDiagnostics);
 
   List<Uri> libraries = <Uri>[];
   memorySourceFiles.forEach((String path, _) {
     libraries.add(new Uri(scheme: 'memory', path: path));
   });
 
   return analyze(libraries, libraryRoot, packageRoot,
                  provider, handler, options);
 }