def _fix_filename(filename):
  """Return a filename which we can use to identify the file.

  The file paths printed by llvm-cov take the form:

      /path/to/repo/out/dir/../../src/filename.cpp

  And then they're truncated to 22 characters with leading ellipses:

      ...../../src/filename.cpp

  This makes it really tough to determine whether the file actually belongs in
  the Skia repo.  This function strips out the leading junk so that, if the file
  exists in the repo, the returned string matches the end of some relative path
  in the repo. This doesn't guarantee correctness, but it's about as close as
  we can get.
  """
  return filename.split('..')[-1].lstrip('./')