Make check_gn_headers.py run on Windows

BUG=661774

Review-Url: https://codereview.chromium.org/2914323002
Cr-Commit-Position: refs/heads/master@{#478848}


CrOS-Libchrome-Original-Commit: 97580dea9404ad2c8b7916cdf3f5f30670f3d226
2 files changed
tree: 56c70462a9be1de8a9d3b8efae92e366d6078603
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/