Recognize new Operating System: NetBSD

NetBSD is BSD and POSIX-like OS.

BUG=

Review-Url: https://codereview.chromium.org/2195203002
Cr-Commit-Position: refs/heads/master@{#408895}
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 4521c6b..fde5a12f5 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -311,6 +311,7 @@
     'OS_NACL',
     'OS_NACL_NONSFI',
     'OS_NACL_SFI',
+    'OS_NETBSD',
     'OS_OPENBSD',
     'OS_POSIX',
     'OS_QNX',