message: Update mixins (copying ones removed by Chromium).
  Cr-Commit-Position: refs/heads/main@{#38629}
diff: }
  }
  },
  + 'hammerhead': {
  + 'swarming': {
  + 'dimensions': {
  + 'device_type': 'hammerhead',
  + 'os': 'Android'
  + }
  + }
  + },
  'ios-device-15.7': {
  'swarming': {
  'dimensions': {
  }
  }
  },
  + 'marshmallow_generic': {
  + 'swarming': {
  + 'dimensions': {
  + 'device_os': 'M'
  + }
  + }
  + },
  'perf-low-bandwidth-audio-perf-test': {
  'merge': {
  'script': '//tools_webrtc/perf/process_perf_results.py',
  