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

mojo/public/tools/bindings/mojom.gni

Index: mojo/public/tools/bindings/mojom.gni
diff --git a/mojo/public/tools/bindings/mojom.gni b/mojo/public/tools/bindings/mojom.gni
index 5cfd5cd7cbb28d7451b8120b5860ec0a80d86899..dd68501d8601f2aeb78979ec13438b694e2388a0 100644
--- a/mojo/public/tools/bindings/mojom.gni
+++ b/mojo/public/tools/bindings/mojom.gni
@@ -334,7 +334,14 @@ template("mojom") {
       output,
     ]
 
-    rebase_base_dir = rebase_path("$root_build_dir/gen/", root_build_dir)
+    invoker_base_dir = ""
+    if (defined(invoker.base_dir)) {
+      invoker_base_dir =
+          rebase_path(invoker.base_dir, "$root_build_dir/../../", ".")
+    }
+
+    rebase_base_dir =
+        rebase_path("$root_build_dir/gen/$invoker_base_dir", root_build_dir)
     if (defined(invoker.sources)) {
       rebase_inputs = rebase_path(inputs, root_build_dir)
     }