Revert "Make VM resolvePackageUri fail on package:foo and package:/foo."

tests/standalone/packages_file_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:async";
 import "dart:io";
 import "dart:convert" show JSON;
 import "package:path/path.dart" as p;
 import "package:async_helper/async_helper.dart";
 
@@ skipping 278 matching lines @@
     // value of these, you can only change what value to expect.
     // For values not included here (commented out), the result is not tested
     // unless a value (maybe null) is provided.
     fixPaths(expect);
 
     expect = {
       "pconf":    null,
       "proot":    null,
       "iconf":    null,
       "iroot":    null,
-      "foo":      null,
+      // "foo":     null,
       "foo/":     null,
       "foo/bar":  null,
       "foo.x":    "qux",
       "bar/bar":  null,
       "relative": "relative/path",
       "nonpkg":   "http://example.org/file"
     }..addAll(expect ?? const {});
 
     // Add http files to the http server.
     if (http.isNotEmpty) {
@@ skipping 674 matching lines @@
 void insertFileAt(Map file, Map http,
                   String path, String name, String content) {
   var parts = path.split('/').toList();
   var dir = (parts[0] == "%file") ? file : http;
   for (var i = 1; i < parts.length - 1; i++) {
     var entry = parts[i];
     dir = dir[entry] ?? (dir[entry] = {});
   }
   dir[name] = content;
 }