Add swarming support for MB (and the GN bots) in the chromium recipes.

scripts/slave/recipes/chromium.expected/full_chromium_perf_Linux_Perf__4_.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.perf",
       "--builder",
       "Linux Perf (4)",
@@ skipping 98 matching lines @@
     "name": "get compile targets for scripts",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "[BUILD]/scripts/slave/cleanup_temp.py"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "cleanup_temp"
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
       "\nimport os, sys\nfrom common import chromium_utils\n\nif os.path.exists(sys.argv[1]):\n  chromium_utils.RemoveDirectory(sys.argv[1])\n",
       "[SLAVE_BUILD]/src/out/Release"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "rmtree build directory",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import os, sys@@@",
       "@@@STEP_LOG_LINE@python.inline@from common import chromium_utils@@@",
       "@@@STEP_LOG_LINE@python.inline@@@@",
@@ skipping 16 matching lines @@
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"buildername\": \"Linux Perf (4)\", \"buildnumber\": 571, \"mastername\": \"chromium.perf\", \"parent_build_archive_url\": \"gs://test-domain/test-archive.zip\", \"parent_buildername\": \"Linux Builder\", \"parent_got_revision\": \"1111111\", \"recipe\": \"chromium\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "extract build"
   },
   {
     "cmd": [
       "python",
       "-u",
+      "[BUILD]/scripts/slave/cleanup_temp.py"
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "cleanup_temp"
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "[SLAVE_BUILD]/src/tools/perf/run_benchmark",
       "list",
       "--browser",
       "release",
       "--json-output",
       "/path/to/tmp/json",
       "--num-shards",
       "5"
     ],
     "cwd": "[SLAVE_BUILD]",
@@ skipping 20 matching lines @@
       "@@@STEP_LOG_LINE@json.output@      \"device_affinity\": 1, @@@",
       "@@@STEP_LOG_LINE@json.output@      \"perf_dashboard_id\": \"dromaeo.cssqueryjquery\"@@@",
       "@@@STEP_LOG_LINE@json.output@    }@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"version\": 2@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   }
 ]