Specify symbol_level 0 for chromeos trybot

This is for faster link time on compile and isolate tests step of linux-chromeos-rel builder

Link time comparison of some binaries between this tryjob, https://ci.chromium.org/b/8943035780027076400 [1]
and https://ci.chromium.org/b/8943036433296462960 [2] is like below.

browser_tests: 54.076s -> 31.285s
unit_tests: 1m49.235s -> 34.616s
components_unittests: 1m36.197s -> 29.543s


isolate tests step time is reduced from 6 mins 12 secs to 2 mins 10 secs.

[1] https://chromium-build-stats.appspot.com/ninja_log/2018/06/22/swarm1444-c4/ninja_log.swarm1444-c4.chrome-bot.20180622-013034.23287.gz/table?dedup=true
[2] https://chromium-build-stats.appspot.com/ninja_log/2018/06/22/swarm1476-c4/ninja_log.swarm1476-c4.chrome-bot.20180622-005824.18926.gz/table?dedup=true

Bug: 794423
Change-Id: I09981de84d2ab3cc9a7a63a599f2284781f71368
Reviewed-on: https://chromium-review.googlesource.com/1111757
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569601}

tools/mb/mb_config.pyl

@@ -1070,7 +1070,7 @@
     ],
 
     'chromeos_with_codecs_release_trybot': [
-      'chromeos_with_codecs', 'release_trybot', 'use_vaapi',
+      'chromeos_with_codecs', 'release_trybot', 'use_vaapi', 'no_symbols',
     ],
 
     'clang_release_bot_minimal_symbols_x86': [