Extend chromium_tests trigger to work across masters.

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 163 matching lines @@
       "--clobber",
       "--",
       "chromium_builder_asan"
     ],
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
     },
     "name": "compile"
   },
   {
+    "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\\Release",
       "/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
   }
 ]