Enable mash_unittests on CrOS Ozone trybot.

testing/buildbot/chromium.chromiumos.json

 {
   "Linux ChromiumOS Builder": {
     "additional_compile_targets": [
       "All"
     ]
   },
   "Linux ChromiumOS Ozone Tests (1)": {
     "gtest_tests": [
       {
         "swarming": {
@@ skipping 203 matching lines @@
         },
         "test": "ipc_tests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "jingle_unittests"
       },
       {
+        "args": [
+          "--override-use-gl-with-osmesa-for-tests"
+        ],
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "mash_unittests"
+      },
+      {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "media_blink_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "media_unittests"
@@ skipping 908 matching lines @@
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "wm_unittests"
       }
     ]
   }
 }