[mojo] Use a pipe path to initialise Mojo in elevated utility processes.

mojo/edk/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.
 
 source_set("headers") {
   sources = [
     "configuration.h",
     "embedder.h",
     "embedder_internal.h",
+    "named_platform_channel_pair.h",
     "platform_channel_pair.h",
     "platform_handle.h",
     "platform_handle_utils.h",
     "process_delegate.h",
     "scoped_platform_handle.h",
   ]
 
   public_deps = [
     "//base",
     "//mojo/public/cpp/system",
@@ skipping 45 matching lines @@
 
 source_set("platform") {
   # This isn't really a standalone target; it must be linked into the
   # mojo_system_impl component.
   visibility = [
     ":embedder",
     "//mojo/edk/system",
   ]
 
   sources = [
+    "named_platform_channel_pair.h",
+    "named_platform_channel_pair_win.cc",
     "platform_channel_pair.cc",
     "platform_channel_pair.h",
     "platform_channel_pair_posix.cc",
     "platform_channel_pair_win.cc",
     "platform_channel_utils_posix.cc",
     "platform_channel_utils_posix.h",
     "platform_handle.cc",
     "platform_handle.h",
     "platform_handle_utils.h",
     "platform_handle_utils_posix.cc",
@@ skipping 56 matching lines @@
 
   deps = [
     "//base",
     "//base/test:test_support",
     "//mojo/edk/system",
     "//mojo/edk/system:test_utils",
     "//mojo/edk/test:test_support",
     "//testing/gtest",
   ]
 }