Do not start goma in ChromeOS gclient runhook if gomadir is given.

scripts/slave/recipes/chromium_trybot.expected/chromeos_analyze.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/chromeos_amd64_generic_chromium_compile_only_ng",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 177 matching lines @@
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[depot_tools]/cros",
       "chrome-sdk",
       "--board=amd64-generic",
       "--nocolor",
       "--use-external-config",
       "--clear-sdk-cache",
       "--gomadir",
       "[CACHE]/cipd/goma",
+      "--nostart-goma",
       "--fastbuild",
       "--",
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[BUILDER_CACHE]/chromeos_amd64_generic_chromium_compile_only_ng/src",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
@@ skipping 82 matching lines @@
   },
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[depot_tools]/cros",
       "chrome-sdk",
       "--board=amd64-generic",
       "--nocolor",
       "--use-external-config",
       "--gomadir",
       "[CACHE]/cipd/goma",
+      "--nostart-goma",
       "--fastbuild",
       "--",
       "python",
       "-u",
       "[BUILDER_CACHE]/chromeos_amd64_generic_chromium_compile_only_ng/src/tools/mb/mb.py",
       "analyze",
       "-m",
       "tryserver.chromium.linux",
       "-b",
       "chromeos_amd64-generic_chromium_compile_only_ng",
@@ skipping 34 matching lines @@
       "import sys; sys.exit(0)"
     ],
     "name": "mark: before_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]