chromium_tests: apply chromium.get_env() when running tests

scripts/slave/recipes/chromium.expected/full_chromium_perf_Linux_Perf__3_.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.perf",
       "--builder",
       "Linux Perf (3)",
@@ skipping 253 matching lines @@
       "-u",
       "[SLAVE_BUILD]/src/tools/perf/run_benchmark",
       "list",
       "--browser",
       "release",
       "--json-output",
       "/path/to/tmp/json",
       "--num-shards",
       "5"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
+    },
     "name": "List Perf Tests",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"steps\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"blink_perf.all.exact\": {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"cmd\": \"/usr/bin/python /path/to/run_benchmark --a=1 -v --b=2\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"device_affinity\": 1, @@@",
       "@@@STEP_LOG_LINE@json.output@      \"perf_dashboard_id\": \"blink_perf.all\"@@@",
       "@@@STEP_LOG_LINE@json.output@    }, @@@",
       "@@@STEP_LOG_LINE@json.output@    \"blink_perf.all.release\": {@@@",
@@ skipping 20 matching lines @@
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]