Add a draft of traversing visitor which will analyse function.

lib/compiler/implementation/dart_backend/dart_backend.dart

Index: lib/compiler/implementation/dart_backend/dart_backend.dart
diff --git a/lib/compiler/implementation/dart_backend/dart_backend.dart b/lib/compiler/implementation/dart_backend/dart_backend.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1e6b66efe8f51c75e757b7c5065e4e5e91eeecc4
--- /dev/null
+++ b/lib/compiler/implementation/dart_backend/dart_backend.dart
@@ -0,0 +1,10 @@
+// Copyright (c) 2012, 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.
+
+#library('dart_backend');
+
+#import('../leg.dart');
+#import('../tree/tree.dart');
+
+#source('backend.dart');