chromium_tests: make IsolatedScript use run_isolated directly, not runtest

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.linux",
       "--builder",
       "Linux Tests",
@@ skipping 187 matching lines @@
       "@@@STEP_LOG_LINE@json.output@  \"dummy_target_2\": \"[dummy hash for dummy_target_2]\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@SET_BUILD_PROPERTY@swarm_hashes@{\"dummy_target_1\": \"[dummy hash for dummy_target_1]\", \"dummy_target_2\": \"[dummy hash for dummy_target_2]\"}@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[SLAVE_BUILD]/src/infra/scripts/runtest_wrapper.py",
-      "--path-build",
-      "[BUILD]",
-      "--",
-      "--target",
-      "Release",
-      "--xvfb",
-      "--factory-properties",
-      "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Tests\", \"buildnumber\": 571, \"mastername\": \"chromium.linux\", \"parent_buildername\": \"Linux Builder\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"swarm_hashes\": {\"telemetry_gpu_unittests\": \"eeeeeeeeeeeeeeeeeeeeeeeeeeeeee\"}, \"workdir\": \"/path/to/workdir/TestSlavename\"}",
-      "--build-properties",
-      "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Tests\", \"buildnumber\": 571, \"mastername\": \"chromium.linux\", \"parent_buildername\": \"Linux Builder\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"swarm_hashes\": {\"telemetry_gpu_unittests\": \"eeeeeeeeeeeeeeeeeeeeeeeeeeeeee\"}, \"workdir\": \"/path/to/workdir/TestSlavename\"}",
-      "--test-type=telemetry_gpu_unittests",
-      "--step-name=telemetry_gpu_unittests",
-      "--builder-name=Linux Tests",
-      "--slave-name=TestSlavename",
-      "--build-number=571",
-      "--run-python-script",
       "[SLAVE_BUILD]/src/tools/swarming_client/run_isolated.py",
       "--isolated",
       "eeeeeeeeeeeeeeeeeeeeeeeeeeeeee",
       "-I",
       "https://isolateserver.appspot.com",
+      "--verbose",
       "--",
       "--isolated-script-test-output",
       "/path/to/tmp/json"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "telemetry_gpu_unittests",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"failures\": [], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"valid\": true@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   }
 ]