Make //mojo/edk/js a component.

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.
 
 # TODO(hansmuller): The organization of tests in this directory is weird:
 #   * Really, js_unittests tests public stuff, so that should live in public
 #     and be reworked as some sort of apptest.
 #   * Both js_unittests and js_integration_tests should auto-generate their
 #     tests somehow. The .cc files are just test runner stubs, including
 #     explicit lists of .js files.
 group("tests") {
   testonly = true
   deps = [
     "test:js_integration_tests",
     "test:js_unittests",
   ]
 }
 
-source_set("js") {
+component("js") {
   sources = [
     "core.cc",
     "core.h",
     "drain_data.cc",
     "drain_data.h",
     "handle.cc",
     "handle.h",
     "handle_close_observer.h",
+    "js_export.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/cpp/system",
   ]
+  defines = [ "MOJO_JS_IMPLEMENTATION" ]
 }