Extensions: Pass current channel and feature session type to extension unpack utility process.

extensions/common/feature_channel_param_traits.h

Index: extensions/common/feature_channel_param_traits.h
diff --git a/extensions/common/feature_channel_param_traits.h b/extensions/common/feature_channel_param_traits.h
new file mode 100644
index 0000000000000000000000000000000000000000..622c61578a3dbe75890096e5827cfe85d8e682fc
--- /dev/null
+++ b/extensions/common/feature_channel_param_traits.h
@@ -0,0 +1,11 @@
+// Copyright 2017 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.
+
+// Multiply-included header, hence no include guard.
+
+#include "components/version_info/version_info.h"
+#include "ipc/ipc_message_macros.h"
+#include "ipc/param_traits_macros.h"
+
+IPC_ENUM_TRAITS_MAX_VALUE(version_info::Channel, version_info::Channel::STABLE)

[dcheng, 2017/06/24 03:30:53]

Hmm. Do we want to put everything in separate files here? I wonder if we just
want to have a common param traits for enums?

[karandeepb, 2017/06/26 21:51:54]

I feel this is better than having a single common param traits file, since this
allows for more granularity, which is needed for example while specifying
"traits_headers" in mojo typemaps.

[dcheng1, 2017/06/26 22:09:49]

There's something to be said for granularity, but it also results in more
multiply included headers proliferating and the amount of boilerplate that needs
to be used to make all the more granular include files get preprocessed
correctly.

Unless there's a need to expose this outside of extensions (which there doesn't
appear to be), just keeping it in the original location seems good enough to
me...

[karandeepb, 2017/06/26 22:16:44]

"just keeping it in the original location" -> This isn't clear to me. I am
assuming you don't mean extension_messages.h since these need to be shared with
mojo? 
I'll introduce a new file to hold these enums though.

[dcheng1, 2017/06/26 23:07:35]

sgtm