In webkitpy/tool/commands/rebaseline.py and related files, there are a bunch of places where a variable called test_prefix_list is used:

https://cs.chromium.org/search/?q=test_prefix_list&sq=package:chromium&type=cs

These are expected to have a certain structure, which is:

  {
    <test or test prefix>: {
      <builder>: <collection of file extensions of new baselines>
    }
  }

Instead of passing around dicts of this format, it would be nice to have a class to represent this. This would hopefully make the code more readable and more easily changeable.