Fix a crash.

test/package_root_info_test.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 file.
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
 import 'package:package_resolver/package_resolver.dart';
 
 void main() {
   var resolver;
   setUp(() {
     resolver = new SyncPackageResolver.root("file:///foo/bar");
   });
 
   group("constructor", () {
     test("with a URI object", () {
       var resolver =
           new SyncPackageResolver.root(Uri.parse("file:///foo/bar/"));
       expect(resolver.packageRoot, equals(Uri.parse("file:///foo/bar/")));
     });
 
+    test("with a URI without a path component", () {
+      var resolver =
+          new SyncPackageResolver.root(Uri.parse("http://localhost:1234"));
+      expect(resolver.packageRoot, equals(Uri.parse("http://localhost:1234/")));
+    });
+
     test("with an invalid URI type", () {
       expect(() => new SyncPackageResolver.root(12), throwsArgumentError);
     });
   });
 
   test("exposes a null config map", () {
     expect(resolver.packageConfigMap, isNull);
   });
 
   test("exposes a null config URI", () {
@@ skipping 103 matching lines @@
       expect(resolver.packagePath("foo"), equals(p.join(sandbox, "foo")));
       expect(resolver.packagePath("bar"), isNull);
     });
 
     test("without a file: scheme", () {
       var resolver = new SyncPackageResolver.root("http://dartlang.org/bar");
       expect(resolver.packagePath("foo"), isNull);
     });
   });
 }