Fix tests that invoke Dart explicitly.

test/runner/runner_test.dart

Index: test/runner/runner_test.dart
diff --git a/test/runner/runner_test.dart b/test/runner/runner_test.dart
index 8817b8b17001f2dff58a35dd28ed0ddb58a6b988..f39987bb2debf72ff82a54665e2e929057bc4bef 100644
--- a/test/runner/runner_test.dart
+++ b/test/runner/runner_test.dart
@@ -281,10 +281,7 @@ $_usage""");
 
     test("directly", () {
       d.file("test.dart", _success).create();
-      var test = runDart([
-        "--package-root=${p.join(packageDir, 'packages')}",
-        "test.dart"
-      ]);
+      var test = runDart(["test.dart"]);
 
       test.stdout.expect(consumeThrough(contains("All tests passed!")));
       test.shouldExit(0);
@@ -331,10 +328,7 @@ $_usage""");
 
     test("directly", () {
       d.file("test.dart", _failure).create();
-      var test = runDart([
-        "--package-root=${p.join(packageDir, 'packages')}",
-        "test.dart"
-      ]);
+      var test = runDart(["test.dart"]);
       test.stdout.expect(consumeThrough(contains("Some tests failed.")));
       test.shouldExit(255);
     });