Extend chromium_tests trigger to work across masters.

scripts/slave/recipes/chromium.expected/full_client_v8_fyi_Chromium_ASAN___debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.v8.fyi",
       "--builder",
       "Chromium ASAN - debug",
@@ skipping 262 matching lines @@
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   },
   {
+    "cmd": [],
+    "name": "trigger"
+  },
+  {
     "cmd": [
       "python",
       "-u",
       "\nimport json, os, sys\nif os.path.exists(sys.argv[1]) and os.path.isdir(sys.argv[1]):\n  with open(sys.argv[2], 'w') as f:\n    json.dump(os.listdir(sys.argv[1]), f)\n",
       "[SLAVE_BUILD]/src/out/Debug",
       "/path/to/tmp/json"
     ],
     "name": "listdir build_dir",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@[@@@",
@@ skipping 59 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@os.remove(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]