Don't use 'interface' in test files.

compiler/javatests/com/google/dart/compiler/resolver/ClassImplementsUnknownInterfaceNegativeTest.dart

Index: compiler/javatests/com/google/dart/compiler/resolver/ClassImplementsUnknownInterfaceNegativeTest.dart
diff --git a/compiler/javatests/com/google/dart/compiler/resolver/ClassImplementsUnknownInterfaceNegativeTest.dart b/compiler/javatests/com/google/dart/compiler/resolver/ClassImplementsUnknownInterfaceNegativeTest.dart
deleted file mode 100644
index 94ed0c82294e9989258f63696c069cfe3d0056f0..0000000000000000000000000000000000000000
--- a/compiler/javatests/com/google/dart/compiler/resolver/ClassImplementsUnknownInterfaceNegativeTest.dart
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright (c) 2011, 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.
-
-// Expect error - Base is not an interface.
-
-interface I {
-}
-
-interface I extends UNKNOWN;