Add string mapping for INVALIDATOR_SHUTTING_DOWN.

Add string mapping for INVALIDATOR_SHUTTING_DOWN.

It looks like this was just an oversight as part of
http://crrev.com/1380103004. Without this debug Windows
builds occasionally pop up alert dialog on shutdown.

BUG=546640
Committed: https://crrev.com/356bb8904a7a195ed7c500b35f37df7ad0b443c8
Cr-Commit-Position: refs/heads/master@{#358419}

[wkorman, 2015-11-06 19:12:24]

wkorman@chromium.org changed reviewers:
+ dcheng@chromium.org, pavely@chromium.org

[wkorman, 2015-11-06 19:12:25]

Small debug assert failing, noticed while working on unrelated
ScopedTempDir issue.

[dcheng, 2015-11-06 20:52:12]

lgtm

[wkorman, 2015-11-06 20:55:59]

The CQ bit was checked by wkorman@chromium.org

[commit-bot: I haz the power, 2015-11-06 21:03:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1414033013/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1414033013/1

[commit-bot: I haz the power, 2015-11-06 22:01:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-06 22:02:06]

Patchset 1 (id:??) landed as
https://crrev.com/356bb8904a7a195ed7c500b35f37df7ad0b443c8
Cr-Commit-Position: refs/heads/master@{#358419}