Use loadable module instead of shared library.

mojo/environment/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.
 
 # GYP version: mojo.gyp:mojo_environment_chromium
 static_library("chromium") {
   output_name = "mojo_environment_chromium"
 
   sources = [
     "environment.cc",
@@ skipping 17 matching lines @@
   output_name = "mojo_environment_impl"
   visibility = "//mojo/*"
 
   sources = [
     "default_async_waiter_impl.cc",
     "default_async_waiter_impl.h",
     "default_logger_impl.cc",
     "default_logger_impl.h",
   ]
 
-  defines = [
-    "MOJO_ENVIRONMENT_IMPL_IMPLEMENTATION",
-  ]
-
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//mojo/common",
   ]
 }