Roll recipe dependencies (nontrivial).

scripts/slave/recipes/dart/sdk_trigger.expected/sdk-trigger-be.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "import time; time.sleep(900)"
     ],
     "name": "wait 15 minutes",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@import time; time.sleep(900)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
-    "cmd": [],
     "name": "trigger",
     "trigger_specs": [
       {
         "builder_name": "dart2js-linux-drt-1-2-be"
       },
       {
         "builder_name": "dart2js-linux-drt-2-2-be"
       },
       {
         "builder_name": "dart2js-linux-drt-csp-minified-be"
@@ skipping 116 matching lines @@
     "~followup_annotations": [
       "@@@STEP_TEXT@analyzer-linux-release-be<br />analyzer-mac10.11-release-be<br />analyzer-win7-release-be<br />dart2js-linux-chromeff-1-4-be<br />dart2js-linux-chromeff-2-4-be<br />dart2js-linux-chromeff-3-4-be<br />dart2js-linux-chromeff-4-4-be<br />dart2js-linux-d8-hostchecked-1-5-be<br />dart2js-linux-d8-hostchecked-2-5-be<br />dart2js-linux-d8-hostchecked-3-5-be<br />dart2js-linux-d8-hostchecked-4-5-be<br />dart2js-linux-d8-hostchecked-5-5-be<br />dart2js-linux-d8-minified-1-5-be<br />dart2js-linux-d8-minified-2-5-be<br />dart2js-linux-d8-minified-3-5-be<br />dart2js-linux-d8-minified-4-5-be<br />dart2js-linux-d8-minified-5-5-be<br />dart2js-linux-drt-1-2-be<br />dart2js-linux-drt-2-2-be<br />dart2js-linux-drt-csp-minified-be<br />dart2js-linux-jsshell-1-4-be<br />dart2js-linux-jsshell-2-4-be<br />dart2js-linux-jsshell-3-4-be<br />dart2js-linux-jsshell-4-4-be<br />dart2js-mac10.11-chrome-be<br />dart2js-mac10.11-safari-1-3-be<br />dart2js-mac10.11-safari-2-3-be<br />dart2js-mac10.11-safari-3-3-be<br />dart2js-win7-ie10chrome-1-4-be<br />dart2js-win7-ie10chrome-2-4-be<br />dart2js-win7-ie10chrome-3-4-be<br />dart2js-win7-ie10chrome-4-4-be<br />dart2js-win7-ie11ff-1-4-be<br />dart2js-win7-ie11ff-2-4-be<br />dart2js-win7-ie11ff-3-4-be<br />dart2js-win7-ie11ff-4-4-be<br />dart2js-win8-ie10-be<br />dart2js-win8-ie11-be<br />pkg-linux-release-be<br />pkg-mac10.11-release-be<br />pkg-win7-release-be@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]