Stub in more IPC attachment brokering functionality.

ipc/BUILD.gn

Index: ipc/BUILD.gn
diff --git a/ipc/BUILD.gn b/ipc/BUILD.gn
index f5f65950e78f9e600a4ba8d98d3d5109e2481528..60fcf283d61e25d2ff5349cc3a1c7399e384bb81 100644
--- a/ipc/BUILD.gn
+++ b/ipc/BUILD.gn
@@ -7,10 +7,12 @@ import("//testing/test.gni")
 component("ipc") {
   sources = [
     "attachment_broker.h",
+    "attachment_broker_messages.h",
     "attachment_broker_win.cc",
     "attachment_broker_win.h",
     "brokerable_attachment.cc",
     "brokerable_attachment.h",
+    "handle_attachment_win.cc",
     "handle_attachment_win.h",
     "ipc_channel.cc",
     "ipc_channel.h",
@@ -32,6 +34,8 @@ component("ipc") {
     "ipc_export.h",
     "ipc_forwarding_message_filter.cc",
     "ipc_forwarding_message_filter.h",
+    "ipc_handle_win.cc",
+    "ipc_handle_win.h",
     "ipc_listener.h",
     "ipc_logging.cc",
     "ipc_logging.h",
@@ -41,6 +45,8 @@ component("ipc") {
     "ipc_message_attachment.h",
     "ipc_message_attachment_set.cc",
     "ipc_message_attachment_set.h",
+    "ipc_message_generator.cc",
+    "ipc_message_generator.h",
     "ipc_message_macros.h",
     "ipc_message_start.h",
     "ipc_message_utils.cc",