Dart: Add warning to the top of .mojom.dart files

mojo/public/tools/bindings/generators/dart_templates/module.lib.tmpl

Index: mojo/public/tools/bindings/generators/dart_templates/module.lib.tmpl
diff --git a/mojo/public/tools/bindings/generators/dart_templates/module.lib.tmpl b/mojo/public/tools/bindings/generators/dart_templates/module.lib.tmpl
index 97db60032f0191066c0fc9ae6e406ae05e960a29..4f1ac2087f26eb5aea8579de75435d8239b87562 100644
--- a/mojo/public/tools/bindings/generators/dart_templates/module.lib.tmpl
+++ b/mojo/public/tools/bindings/generators/dart_templates/module.lib.tmpl
@@ -1,6 +1,8 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
+{#- Copyright 2014 The Chromium Authors. All rights reserved. -#}
+{#- Use of this source code is governed by a BSD-style license that can be -#}
+{#- found in the LICENSE file. -#}
+// WARNING: DO NOT EDIT. This file was generated by a program.
+// See $MOJO_SDK/tools/bindings/mojom_bindings_generator.py.
 
 library {{module.name|dot_to_underscore}};