Use Fasta scanner when running analyzer.

pkg/testing/lib/src/discover.dart

 // Copyright (c) 2016, 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.md file.
 
 library testing.discover;
 
 import 'dart:io' show Directory, FileSystemEntity, Platform, Process;
 
 import 'dart:async' show Future, Stream, StreamController, StreamSubscription;
 
 import '../testing.dart' show TestDescription;
 
 final Uri packageConfig = computePackageConfig();
 
 final Uri dartSdk = computeDartSdk();
 
 /// Common arguments when running a dart program. Returns a copy that can
 /// safely be modified by caller.
-List<String> get dartArguments => <String>["-c", "--packages=$packageConfig"];
+List<String> get dartArguments =>
+    <String>["-c", "--packages=${packageConfig.toFilePath()}"];
 
 Stream<TestDescription> listTests(List<Uri> testRoots, {Pattern pattern}) {
   StreamController<TestDescription> controller =
       new StreamController<TestDescription>();
   Map<Uri, StreamSubscription> subscriptions = <Uri, StreamSubscription>{};
   for (Uri testRootUri in testRoots) {
     subscriptions[testRootUri] = null;
     Directory testRoot = new Directory.fromUri(testRootUri);
     testRoot.exists().then((bool exists) {
       if (exists) {
@@ skipping 45 matching lines @@
 Future<Process> startDart(Uri program,
     [List<String> arguments, List<String> vmArguments]) {
   List<String> allArguments = <String>[];
   allArguments.addAll(vmArguments ?? dartArguments);
   allArguments.add(program.toFilePath());
   if (arguments != null) {
     allArguments.addAll(arguments);
   }
   return Process.start(Platform.resolvedExecutable, allArguments);
 }