Add include_unwind_tables to the linux-chromeos-chrome bot.

include_unwind_tables was removed from this bot a while ago when
binary size metrics were spun up for fear that the tables would inflate
the binaries.

However, we don't actually ship linux-chromeos binaries, so their size
metrics aren't very representative. Plus, the lack of the tables makes
sheriffing more difficult since test failures won't produce full stack
traces.

Adding the tables back to the bot should make sheriffing it easier.

Bug: None
Change-Id: I67e042dfd1640d014fad62b741966ee211bb557f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2419002Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808502}

tools/mb/mb_config.pyl

@@ -24,7 +24,7 @@
       'linux-chrome': 'official_goma',
       'linux-chrome-beta': 'official_goma',
       'linux-chrome-stable': 'official_goma',
-      'linux-chromeos-chrome': 'official_goma_chromeos',
+      'linux-chromeos-chrome': 'official_goma_chromeos_include_unwind_tables',
       'linux-chromeos-chrome-easwa': 'official_goma_chromeos',
       'mac-chrome': 'official_goma_mac',
       'mac-chrome-beta': 'official_goma_mac',