crash-reporter: Add session_manager logs to Chrome crashes.

Attach the last twenty session_manager messages from
/var/log/messages to Chrome crash reports.

BUG=chromium:233833
TEST=manual: triggered a crash and checked chrome.txt in the
     crash report (1f8c6ff259947e7a)

Change-Id: I733b448ccc6e01111556a5a632e185cc58dfd917
Reviewed-on: https://chromium-review.googlesource.com/243378
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>

crash_reporter/crash_reporter_logs.conf

@@ -14,15 +14,17 @@
 # occurred and we should avoid running anything that might cause
 # another crash.  Similarly these command block the notification of
 # the crash to parent processes, so commands should execute quickly.
-#
+# Commands cannot contain colons.
+
 update_engine:cat $(ls -1tr /var/log/update_engine | tail -5 | sed s.^./var/log/update_engine/.) | tail -c 50000
+
 # The cros_installer output is logged into the update engine log file,
 # so it is handled in the same way as update_engine.
 cros_installer:cat $(ls -1tr /var/log/update_engine | tail -5 | sed s.^./var/log/update_engine/.) | tail -c 50000
 
 # Dump the last 20 lines of the last two files in Chrome's system and user log
-# directories.
-chrome:for f in $(ls -1rt /var/log/chrome/chrome_[0-9]* | tail -2) $(ls -1rt /home/chronos/u-*/log/chrome_[0-9]* 2>/dev/null | tail -2); do echo "===$f (tail)==="; tail -20 $f; echo EOF; done
+# directories, along with the last 20 messages from the session manager.
+chrome:for f in $(ls -1rt /var/log/chrome/chrome_[0-9]* | tail -2) $(ls -1rt /home/chronos/u-*/log/chrome_[0-9]* 2>/dev/null | tail -2); do echo "===$f (tail)==="; tail -20 $f; echo EOF; echo; done; echo "===session_manager (tail)==="; awk '$3 ~ "^session_manager\[" { print }' /var/log/messages | tail -20; echo EOF
 
 # The following rule is used for generating additional diagnostics when
 # collection of user crashes fails.  This output should not be too large