Add file system service to Dart's embedder private package

mojo/dart/embedder/BUILD.gn

Index: mojo/dart/embedder/BUILD.gn
diff --git a/mojo/dart/embedder/BUILD.gn b/mojo/dart/embedder/BUILD.gn
index b933f1be91307cc851bd14852ff345b4ef2c09d2..a42b19dfb475e4adf97e177e8bc7c723f00a749b 100644
--- a/mojo/dart/embedder/BUILD.gn
+++ b/mojo/dart/embedder/BUILD.gn
@@ -75,6 +75,7 @@ group("dart_embedder_packages") {
     ":dart_embedder_package_bindings",
     ":dart_embedder_package_network",
     ":dart_embedder_package_network_service",
+    ":dart_embedder_package_files_service",
   ]
 }
 
@@ -98,6 +99,11 @@ dart_embedder_package("dart_embedder_package_network_service") {
   destination = "mojo_services/mojo"
 }
 
+dart_embedder_package("dart_embedder_package_files_service") {
+  package = "mojo/services/files/interfaces"
+  destination = "mojo_services/mojo/files"
+}
+
 action_foreach("dart_embedder_package_sdk") {
   sources = rebase_path(package_mojo_sources + dart_mojo_internal_sdk_sources,
                         "",
@@ -168,6 +174,7 @@ action("generate_snapshot_bin") {
   bindings_mojoms = rebase_path("//mojo/public/interfaces/bindings")
   network_mojoms = rebase_path("//mojo/public/interfaces/network")
   network_service_mojoms = rebase_path("//mojo/services/network/interfaces")
+  files_mojoms = rebase_path("//mojo/services/files/interfaces")
 
   # This script generates --url_mapping command line arguments for all
   # generated mojom.dart bindings files. See HACKING.md for more information.
@@ -182,6 +189,7 @@ action("generate_snapshot_bin") {
                     "$bindings_mojoms,mojo/mojo",
                     "$network_mojoms,mojo/mojo",
                     "$network_service_mojoms,mojo_services/mojo",
+                    "$files_mojoms,mojo_services/mojo/files",
                   ],
                   "list lines")