Teach PRESUBMIT.py how to run gn check for most of the mojo repo

mojo/edk/js/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.
 
 source_set("js") {
   sources = [
     "core.cc",
     "core.h",
     "drain_data.cc",
     "drain_data.h",
     "handle.cc",
     "handle.h",
     "handle_close_observer.h",
     "mojo_runner_delegate.cc",
     "mojo_runner_delegate.h",
     "support.cc",
     "support.h",
     "threading.cc",
     "threading.h",
     "waiting_callback.cc",
     "waiting_callback.h",
   ]
 
   public_deps = [
     "//base",
     "//gin",
     "//v8",
   ]
+
+  deps = [
+    "//mojo/public/c/environment",
+    "//mojo/public/cpp/system",
+  ]
 }
 
 source_set("js_unittests") {
   testonly = true
   deps = [
+    "//base",
     "//mojo/edk/test:test_support",
   ]
 
   sources = [
     "handle_unittest.cc",
   ]
 }