Add extended_error_code to members for URLLoaderCompletionStatus.

It's probably an oversight that this is missing;
also adding a comment to the header file for next time.
Andrey thank you for pointing me at network_param_ipc_traits.h.

R=caseq

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I21e278de132e0b3e465c3e27d25201b6878270e3
Reviewed-on: https://chromium-review.googlesource.com/1038808Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Johannes Henkel <johannes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555539}

services/network/public/cpp/network_param_ipc_traits.h

@@ -282,6 +282,7 @@ IPC_STRUCT_TRAITS_END()
 
 IPC_STRUCT_TRAITS_BEGIN(network::URLLoaderCompletionStatus)
   IPC_STRUCT_TRAITS_MEMBER(error_code)
+  IPC_STRUCT_TRAITS_MEMBER(extended_error_code)
   IPC_STRUCT_TRAITS_MEMBER(exists_in_cache)
   IPC_STRUCT_TRAITS_MEMBER(completion_time)
   IPC_STRUCT_TRAITS_MEMBER(encoded_data_length)

services/network/public/cpp/url_loader_completion_status.h

@@ -17,6 +17,9 @@
 
 namespace network {
 
+// NOTE: When adding/removing fields to this struct, don't forget to
+// update services/network/public/cpp/network_param_ipc_traits.h.
+
 struct COMPONENT_EXPORT(NETWORK_CPP_BASE) URLLoaderCompletionStatus {
   URLLoaderCompletionStatus();
   URLLoaderCompletionStatus(const URLLoaderCompletionStatus& status);