Dart: Removes all but native calls and the handle watcher from the snapshot.

mojo/public/interfaces/application/BUILD.gn

 # 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.
 
 import("../../tools/bindings/mojom.gni")
 
 # GYP version: mojo/public/mojo_public.gyp:mojo_application_bindings
 mojom("application") {
   sources = [
     "application.mojom",
     "service_provider.mojom",
     "shell.mojom",
   ]
+
+  # This base dir ensures that Dart's Mojo SDK can be imported with, e.g.,
+  # import 'package:mojo/public/dart/core.dart' even when the Mojo SDK lives
+  # somewhere else in the source tree.
+  base_dir = mojo_root
 }