Revert of Remove IPC::BrokerableAttachment.

ipc/BUILD.gn

 # Copyright (c) 2012 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.
 
 import("//build/config/nacl/config.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//testing/test.gni")
 import("//tools/ipc_fuzzer/ipc_fuzzer.gni")
 
 component("ipc") {
   sources = [
+    "brokerable_attachment.cc",
+    "brokerable_attachment.h",
     "export_template.h",
     "handle_attachment_win.cc",
     "handle_attachment_win.h",
     "handle_win.cc",
     "handle_win.h",
     "ipc_channel.cc",
     "ipc_channel.h",
     "ipc_channel_common.cc",
     "ipc_channel_factory.cc",
     "ipc_channel_factory.h",
@@ skipping 227 matching lines @@
       ":ipc",
     ]
     deps = [
       "//base",
       "//base/test:test_support",
       "//mojo/edk/test:test_support",
       "//testing/gtest",
     ]
   }
 }