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

mojo/public/dart/BUILD.gn

Index: mojo/public/dart/BUILD.gn
diff --git a/mojo/public/dart/BUILD.gn b/mojo/public/dart/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..4790fec84b74e15ceb289a168baec0383c761c01
--- /dev/null
+++ b/mojo/public/dart/BUILD.gn
@@ -0,0 +1,29 @@
+import("../mojo_sdk.gni")
+import("rules.gni")
+
+dart_mojo_sdk_sources = [
+  "application.dart",
+  "bindings.dart",
+  "core.dart",
+  "src/application_connection.dart",
+  "src/application.dart",
+  "src/buffer.dart",
+  "src/codec.dart",
+  "src/data_pipe.dart",
+  "src/drain_data.dart",
+  "src/event_stream.dart",
+  "src/handle.dart",
+  "src/message.dart",
+  "src/message_pipe.dart",
+  "src/proxy.dart",
+  "src/struct.dart",
+  "src/stub.dart",
+  "src/types.dart",
+]
+
+dart_package("dart") {
+  # This base dir ensures that Dart's Mojo SDK can be imported with, e.g.,
+  # import 'package:mojo/public/dart/core.dart';
+  base_dir = rebase_path("../../$mojo_root", ".", ".")
+  sources = dart_mojo_sdk_sources
+}