[Telemetry] Check whether powermetrics service has already terminated and fail gracefully

testing/buildbot/chromium.mac.json

 {
   "Mac GN": {
     "additional_compile_targets": [
       "gn_all"
     ],
     "gtest_tests": [
       {
         "test": "base_unittests"
       }
     ]
@@ skipping 1166 matching lines @@
     "isolated_scripts": [
       {
         "isolate_name": "telemetry_gpu_unittests",
         "name": "telemetry_gpu_unittests",
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       },
       {
         "isolate_name": "telemetry_perf_unittests",
-        "name": "telemetry_perf_unittests"
+        "name": "telemetry_perf_unittests",
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        }
       }
     ],
     "scripts": [
       {
         "name": "telemetry_unittests",
         "script": "telemetry_unittests.py"
       },
       {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
@@ skipping 281 matching lines @@
         "name": "telemetry_perf_unittests",
         "script": "telemetry_perf_unittests.py"
       },
       {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
       }
     ]
   }
 }