Dart: Reorganize files

mojo/dart/embedder/snapshotter/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.
 
+group("snapshotter") {
+  deps = [
+    ":dart_snapshotter",
+  ]
+}
+
 executable("dart_snapshotter") {
   sources = [
     "main.cc",
     "vm.cc",
     "vm.h",
   ]
 
   deps = [
     "//base",
     "//build/config/sanitizers:deps",
     "//dart/runtime/vm:libdart_platform",
     "//dart/runtime:libdart",
     "//mojo/common",
     "//mojo/dart/embedder:dart_snapshot_cc",
     "//mojo/edk/base_edk",
     "//mojo/edk/system",
     "//mojo/environment:chromium",
     "//mojo/public/cpp/system",
     "//mojo/public/cpp/utility",
     "//mojo/public/interfaces/application",
     "//third_party/zlib",
     "//tonic",
   ]
 }