chromium_tests: apply chromium.get_env() when running tests

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.fyi",
       "--builder",
       "Chromium Linux Goma Canary",
@@ skipping 294 matching lines @@
       "--annotate=gtest",
       "--test-type=base_unittests",
       "--step-name=base_unittests",
       "--test-launcher-summary-output",
       "/path/to/tmp/json",
       "--builder-name=Chromium Linux Goma Canary",
       "--slave-name=TestSlavename",
       "--build-number=571",
       "base_unittests"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "base_unittests"
   },
   {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/runtest.py",
       "--target",
       "Release",
       "--xvfb",
       "--factory-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"build_data_dir\": \"[ROOT]/build_data_dir\", \"buildername\": \"Chromium Linux Goma Canary\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"parent_buildername\": null, \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"build_data_dir\": \"[ROOT]/build_data_dir\", \"buildername\": \"Chromium Linux Goma Canary\", \"buildnumber\": 571, \"mastername\": \"chromium.fyi\", \"parent_buildername\": null, \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
       "--annotate=gtest",
       "--test-type=content_unittests",
       "--step-name=content_unittests",
       "--test-launcher-summary-output",
       "/path/to/tmp/json",
       "--builder-name=Chromium Linux Goma Canary",
       "--slave-name=TestSlavename",
       "--build-number=571",
       "content_unittests"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "content_unittests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]