Add loonybear to chromium user mapping

Change-Id: I00fc70141ef1afe1b926e0f9b72c7055d4d82917
Reviewed-on: https://chromium-review.googlesource.com/965007
Commit-Queue: Luna Lu <loonybear@chromium.org>
Reviewed-by: Luna Lu <loonybear@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543502}

docs/user_handle_mapping.md

@@ -63,6 +63,7 @@ For Chromium contributors that have different nicks on other domains.
 | levin             | dave\_levin     | levin           |
 | lfg               | lfg\_           | lfg             |
 | littledan         | littledan       | dehrenberg      |
+| loonybear         | loonybear       | lunalu          |
 | luken             | luken_chromium  | luken           |
 | mark              | markmentovai    | mmentovai       |
 | mbarbella         | mbarbella       | mbarbella       |