Add landmine after change to messages.h

BUG=N
LOG=N
TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/1174523004

Cr-Commit-Position: refs/heads/master@{#28875}

build/get_landmines.py

@@ -21,6 +21,7 @@ def main():
   print 'Revert activation of MSVS 2013.'
   print 'Activating MSVS 2013 again.'
   print 'Clobber after ICU roll.'
+  print 'Clobber after change to src/messages.h.'
   return 0