Adding Athenas browser and unit tests which are required for running the tests on a buildbot

testing/buildbot/chromium_trybot.json

 {
   "compile_targets": [
     "all"
   ],
   "gtest_tests": [
     "accessibility_unittests",
     "app_list_unittests",
     {
       "test": "ash_unittests",
       "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"],
@@ skipping 187 matching lines @@
       "platforms": ["mac"]
     },
     {
       "test": "chromeos_unittests",
       "platforms": ["linux"],
       "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"]
     },
     {
       "test": "athena_unittests",
       "platforms": ["linux"],
-      "chromium_configs": ["chromium_chromeos", "chromium_chromeos_clang"]
+      "chromium_configs": ["chromium_chromeos_athena"]
     },
     {
       "test": "display_unittests",
       "platforms": ["linux"]
     },
     {
       "test": "ozone_unittests",
       "platforms": ["linux"],
       "chromium_configs": ["chromium_chromeos_ozone"]
     }
   ],
 
   "non_filter_builders": [
   ],
 
   "non_filter_tests_builders": [
   ],
 
   "filter_compile_builders": [
     "win_chromium_compile_dbg",
     "win_chromium_rel_swarming",
     "win_chromium_x64_rel_swarming",
     "win8_chromium_rel"
   ]
 }