PRESUBMIT: Add linux_msan to default trybots.

Will commit as soon it's online.

BUG=
R=pbos@webrtc.org
TBR=niklas.enbom@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/26939004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7523 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index b949951..507af52 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -304,6 +304,7 @@
       'linux',
       'linux_asan',
       'linux_baremetal',
+      'linux_msan',
       'linux_rel',
       'linux_tsan2',
   ] + linux_gn_bots