Fix path.toUri for relative paths.

test/url_test.dart

Index: test/url_test.dart
diff --git a/test/url_test.dart b/test/url_test.dart
index aca161b41e6e6e4a52eb1c1d7a3974bbebc41b00..854e19abd0bb903da404d53f2e5334b009c3decb 100644
--- a/test/url_test.dart
+++ b/test/url_test.dart
@@ -721,6 +721,7 @@ main() {
         Uri.parse('http://dartlang.org/path/to/foo'));
     expect(context.toUri('http://dartlang.org/path/to/foo/'),
         Uri.parse('http://dartlang.org/path/to/foo/'));
+    expect(context.toUri('path/to/foo/'), Uri.parse('path/to/foo/'));
     expect(
         context.toUri('file:///path/to/foo'), Uri.parse('file:///path/to/foo'));
     expect(context.toUri('foo/bar'), Uri.parse('foo/bar'));