Make it obvious when perf tryjob builds fail.

scripts/slave/recipes/bisection/desktop_bisect.expected/basic_perf_tryjob_with_metric.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/linux_perf_bisect",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 654 matching lines @@
       "--host",
       "cr-buildbucket.appspot.com",
       "9016911228971028736"
     ],
     "cwd": "[BUILDER_CACHE]/linux_perf_bisect",
     "name": "buildbucket.get (4)",
     "stdout": "/path/to/tmp/json",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"build\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"result\": \"SUCCESS\"@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"result\": \"SUCCESS\", @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"url\": \"buildbot.dummy.url/job/12\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os, sys\nfrom common import chromium_utils # Error? See https://crbug.com/584783.\n\n\nif os.path.exists(sys.argv[1]):\n  chromium_utils.RemoveDirectory(sys.argv[1])\n",
@@ skipping 111 matching lines @@
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]