Make mojo dart controller depend on tonic and get building without wtf

mojo/dart/embedder/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.
 
 # embedder specific template rules.
 import("embedder.gni")
 
 source_set("dart_controller_no_snapshot") {
   sources = [
     "$target_gen_dir/dart_embedder_patch_resources.cc",
@@ skipping 30 matching lines @@
     ":dart_embedder_packages",
     ":generate_dart_embedder_patch_resources_cc",
     ":generate_dart_embedder_service_isolate_resources_cc",
     "//base",
     "//base:i18n",
     "//dart/runtime:libdart",
     "//dart/runtime/bin:libdart_embedder_noio",
     "//third_party/dart-pkg",
     "//mojo/public/c/system",
     "//mojo/public/cpp/system",
+    "//tonic",
   ]
 
   defines = []
   if (is_debug) {
     defines += [ "DEBUG" ]
   } else {
     defines += [ "NDEBUG" ]
   }
 
   include_dirs = [ "//dart/runtime" ]
@@ skipping 343 matching lines @@
     "--vm_input_bin",
     rebase_path("$target_gen_dir/vm_isolate_snapshot.bin"),
     "--input_bin",
     rebase_path("$target_gen_dir/isolate_snapshot.bin"),
     "--input_cc",
     rebase_path("//mojo/dart/embedder/snapshot.cc.tmpl"),
     "--output",
     rebase_path(output),
   ]
 }