We we use LUCI Scheduler to schedule swarming ChromeOS builds, the swarming recipe crashes.

https://luci-scheduler.appspot.com/jobs/chromeos

This is probably related to differences in how parameters_json is encoded.

Sample crash:
  https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8950052320994990192



Traceback (most recent call last):
  File "/b/swarming/w/ir/kitchen-checkout/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/run.py", line 287, in _new_run
    recipe_result = recipe_script.run(api, self.properties, self.environ)
  File "/b/swarming/w/ir/kitchen-checkout/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/loader.py", line 98, in run
    self.run_steps, properties, environ, self.PROPERTIES, api=api)
  File "/b/swarming/w/ir/kitchen-checkout/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/loader.py", line 626, in invoke_with_properties
    arg_names, **additional_args)
  File "/b/swarming/w/ir/kitchen-checkout/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/loader.py", line 589, in _invoke_with_properties
    return callable_obj(*props, **additional_args)
  File "/b/swarming/w/ir/kitchen-checkout/scripts/slave/recipes/cros/swarming.py", line 20, in RunSteps
    tryjob_args = json.loads(tryjob_args)
  File "/b/swarming/w/ir/cipd_bin_packages/lib/python2.7/json/__init__.py", line 339, in loads
    return _default_decoder.decode(s)
  File "/b/swarming/w/ir/cipd_bin_packages/lib/python2.7/json/decoder.py", line 364, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/b/swarming/w/ir/cipd_bin_packages/lib/python2.7/json/decoder.py", line 382, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded