Fix tests to run in dart-lang/sdk.

test/test_pub.dart

Index: test/test_pub.dart
diff --git a/test/test_pub.dart b/test/test_pub.dart
index 1d72496c4e953ed2736d01b807adebfecd7b77dc..03889c67ffd1c2f36ae8ea272edd62c13f1cdce0 100644
--- a/test/test_pub.dart
+++ b/test/test_pub.dart
@@ -522,8 +522,11 @@ ScheduledProcess startPub({List args, Future<String> tokenEndpoint,
   var pubPath = p.absolute(p.join(pubRoot, 'bin/pub.dart'));
   if (fileExists('$pubPath.snapshot')) pubPath += '.snapshot';
 
-  var dartArgs = [pubPath, '--verbose'];
-  dartArgs.addAll(args);
+  var dartArgs = [
+    '--package-root=${p.toUri(p.absolute(p.fromUri(Platform.packageRoot)))}',
+    pubPath,
+    '--verbose'
+  ]..addAll(args);
 
   if (tokenEndpoint == null) tokenEndpoint = new Future.value();
   var environmentFuture = tokenEndpoint