chromeos-base/protofiles: add missing dependency

Add build dependency on dev-python/six. Normally this package
is available as a part of the SDK but in edge cases like python
version upgrade in the SDK it should be spelled out explicitly.

BUG=b/257113269
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I6b5a033d0627f29491ea45a84caad4d2001b0c4f
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/chromiumos-overlay/+/42400
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
1 file changed