chromium_tests: apply chromium.get_env() when running tests

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 301 matching lines @@
       "--test-launcher-summary-output",
       "/path/to/tmp/json",
       "--generate-json-file",
       "-o",
       "gtest-results/aura_unittests.exe",
       "--builder-name=Win7 Tests (1)",
       "--slave-name=TestSlavename",
       "--build-number=571",
       "aura_unittests.exe"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
+    },
     "name": "aura_unittests"
   },
   {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]\\src\\infra\\scripts\\runtest_wrapper.py",
       "--",
       "--target",
@@ skipping 10 matching lines @@
       "--generate-json-file",
       "-o",
       "gtest-results/browser_tests.exe",
       "--builder-name=Win7 Tests (1)",
       "--slave-name=TestSlavename",
       "--build-number=571",
       "browser_tests.exe",
       "--test-launcher-shard-index=0",
       "--test-launcher-total-shards=2"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
+    },
     "name": "browser_tests"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]\\src\\chrome\\test\\mini_installer\\test_installer.py",
       "--build-dir",
       "[SLAVE_BUILD]\\src\\out",
       "--target",
       "Release",
       "--force-clean",
       "--config",
       "[SLAVE_BUILD]\\src\\chrome\\test\\mini_installer\\config\\config.config",
       "--write-full-results-to",
       "/path/to/tmp/json"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
+    },
     "name": "test_installer"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\process_dumps.py",
       "--target",
       "Release"
     ],
+    "env": {
+      "GOMA_SERVICE_ACCOUNT_JSON_FILE": "C:\\creds\\service_accounts\\service-account-goma-client.json"
+    },
     "name": "process_dumps"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]