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

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

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "chromium.linux",
       "--builder",
       "Linux Tests",
@@ skipping 123 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 15 matching lines @@
       "f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
       "--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\", \"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\", \"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"
+  },
+  {
     "allow_subannotations": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/runtest.py",
       "--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\", \"workdir\": \"/path/to/workdir/TestSlavename\"}",
@@ skipping 49 matching lines @@
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "browser_tests"
   },
   {
     "name": "$final_result",
     "reason": "1 tests failed: ['base_unittests']",
     "status_code": 1
   }
 ]