Handle clash of prefix/non-prefix imports.

tests/language/hidden_import_test.dart

Index: tests/language/hidden_import_test.dart
diff --git a/tests/language/hidden_import_test.dart b/tests/language/hidden_import_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..26be79c6719326dd4bf17582709a1ec90de77880
--- /dev/null
+++ b/tests/language/hidden_import_test.dart
@@ -0,0 +1,17 @@
+// Copyright (c) 2013, 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.
+
+// Tests that dart: imports are implicitly hidden and cause warning on use.
+
+library hidden_import;
+
+import 'hidden_import_lib.dart';
+import 'hidden_import_lib.dart' as prefix;
+import 'dart:async';
+import 'dart:async' as prefix;
+
+main() {
+  new Future(); /// 01: static type warning
+  new prefix.Future(); /// 02: static type warning
+}