Add accessibility_unittests and chromevox_tests to buildbot config.

testing/buildbot/chromium_trybot.json

 {
   "compile_targets": [
     "all"
   ],
   "gtest_tests": [
     "accessibility_unittests",
     "app_list_unittests",
     {
       "test": "base_unittests",
       "swarming": {
         "can_use_on_swarming_builders": true
       }
     },
     {
       "test": "browser_tests",
       "exclude_builders": ["tryserver.chromium:win_chromium_x64_rel"],
       "swarming": {
         "can_use_on_swarming_builders": true,
         "shards": 5
       }
     },
     "cacheinvalidation_unittests",
     "cast_unittests",
     "cc_unittests",
     "chromedriver_unittests",
     {
+      "test": "chromevox_tests",
+      "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"]
+    },
+    {
       "test": "chrome_elf_unittests",
       "platforms": ["win"]
     },
     "components_unittests",
     {
       "test": "compositor_unittests",
       "platforms": ["linux", "win"]
     },
     {
       "test": "courgette_unittests",
@@ skipping 144 matching lines @@
     ".*gyp[i]?",
     "chrome/test/data/.*",
     "content/test/data/.*",
     "DEPS",
     "testing/buildbot/.*"
   ],
 
   "filter_builders": [
   ]
 }