Fix shared_release_trybot build config to actually use "shared" mixin.

Bug: 701825
Change-Id: Ib4e789ec1237782d9a6a65da6c24dac02713095b
Reviewed-on: https://chromium-review.googlesource.com/c/1367870
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Abhishek Arya <inferno@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614770}

tools/mb/mb_config.pyl

@@ -2155,11 +2155,11 @@
     },
 
     'shared_release_bot': {
-      'mixins': ['shared', 'release', 'goma']
+      'mixins': ['shared', 'release', 'goma'],
     },
 
     'shared_release_trybot': {
-      'mixins': ['shared', 'release_trybot', ],
+      'mixins': ['shared_release_bot', 'minimal_symbols', 'dcheck_always_on'],
     },
 
     'static': {