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

mojo/public/interfaces/application/BUILD.gn

Index: mojo/public/interfaces/application/BUILD.gn
diff --git a/mojo/public/interfaces/application/BUILD.gn b/mojo/public/interfaces/application/BUILD.gn
index 463df5580ea631d550faa85ade3fbf914a6b8797..5b15344c5071309d650162230f4a7cafb3a10c5e 100644
--- a/mojo/public/interfaces/application/BUILD.gn
+++ b/mojo/public/interfaces/application/BUILD.gn
@@ -11,4 +11,9 @@ mojom("application") {
     "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
 }