Add a way to set a NotFound HTTP handler.

Add a way to set a NotFound HTTP handler.

BUG=707622
Review-Url: https://codereview.chromium.org/2927093003
Committed: https://github.com/luci/luci-go/commit/f63e083322ae76eca2fe7ef3359dba58742045e4

[dsansome, 2017-06-09 04:42:49]

dsansome@chromium.org changed reviewers:
+ vadimsh@chromium.org

[Vadim Sh., 2017-06-09 19:10:32]

lgtm

[dsansome, 2017-06-13 00:07:21]

The CQ bit was checked by dsansome@chromium.org

[commit-bot: I haz the power, 2017-06-13 00:07:25]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-06-13 00:20:56]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1497312441031190, "parent_rev":
"7e25e6fdad68659a669c8e1569b3eb291639db78", "commit_rev":
"f63e083322ae76eca2fe7ef3359dba58742045e4"}

[commit-bot: I haz the power, 2017-06-13 00:21:00]

Description was changed from

==========
Add a way to set a NotFound HTTP handler.

BUG=707622
==========

to

==========
Add a way to set a NotFound HTTP handler.

BUG=707622

Review-Url: https://codereview.chromium.org/2927093003
Committed:
https://github.com/luci/luci-go/commit/f63e083322ae76eca2fe7ef3359dba58742045e4
==========

[commit-bot: I haz the power, 2017-06-13 00:21:01]

Committed patchset #1 (id:1) as
https://github.com/luci/luci-go/commit/f63e083322ae76eca2fe7ef3359dba58742045e4