Setup ash_unittests --mash

testing/buildbot/chromium.fyi.json

 {
   "Android Asan Builder Tests (dbg)": {
     "gtest_tests": [
       {
         "args": [
           "--tool=asan"
         ],
         "swarming": {
           "can_use_on_swarming_builders": false
         },
@@ skipping 11634 matching lines @@
       }
     ]
   },
   "Mojo ChromiumOS": {
     "additional_compile_targets": [
       "mash:all"
     ],
     "gtest_tests": [
       {
         "args": [
+          "--mash",
+          "--test-launcher-filter-file=../../testing/buildbot/filters/ash_unittests_mash.filter"
+        ],
+        "name": "ash_unittests --mash",
+        "override_isolate_target": "ash_unittests",
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "ash_unittests"
+      },
+      {
+        "args": [
           "--mus",
           "--test-launcher-filter-file=../../testing/buildbot/filters/ash_unittests_mus.filter"
         ],
         "name": "ash_unittests --mus",
         "override_isolate_target": "ash_unittests",
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "ash_unittests"
       },
@@ skipping 1442 matching lines @@
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": false
         },
         "test": "views_unittests"
       }
     ]
   }
 }