Mojo: Make ChromeOS trybot actually use a chromeos config.

Bug: 771381
Change-Id: I42a1b5c2d691e9973f21ac0de8fc441aa9fe3e21
Reviewed-on: https://chromium-review.googlesource.com/699940Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506493}

tools/mb/mb_config.pyl

@@ -624,7 +624,7 @@
       'linux_layout_tests_layout_ng': 'release_bot',
 
       'linux_mojo': 'release_trybot',
-      'linux_mojo_chromeos': 'release_trybot',
+      'linux_mojo_chromeos': 'chromeos_with_codecs_release_trybot',
       'linux_nacl_sdk_build': 'release_bot',
       'linux_nacl_sdk': 'release_bot',
       'linux_optional_gpu_tests_rel': 'gpu_fyi_tests_release_trybot',