Enable ash_unittests for the Ozone ChromiumOS bots

BUG=398888

Review URL: https://codereview.chromium.org/448443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288094 0039d316-1c4b-4281-b951-d872f2087c98

testing/buildbot/chromium.chromiumos.json

@@ -52,6 +52,7 @@
   "Linux ChromiumOS Ozone Tests (1)": {
     "gtest_tests": [
       "accessibility_unittests",
+      "ash_unittests",
       "base_unittests",
       "cacheinvalidation_unittests",
       "chromeos_unittests",