Interesting, this looks like an artefact of the way we build the grok index packs.  I'll look into it.

These files are used to create the Xref index pack, e.g., each .filepaths file lists the files needed to replay the compilation of the corresponding file. They should not be included in the source tar ball used for indexing. 

The fix is simple so I sent out a CL: https://chromium-review.googlesource.com/c/419018/

Note that this does not happen on staging (https://cs-staging.chromium.org/search/?q=.*filepaths+package:%5Echromium$&type=cs), where files are read from the Git repo and the intermediate files are not checked in. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build.git/+/691add00f8f9ba2813e1b3a02bb98c41a38c6556

commit 691add00f8f9ba2813e1b3a02bb98c41a38c6556
Author: Emma Soederberg <emso@chromium.org>
Date: Tue Dec 13 08:34:24 2016

Adds filtering of .filepaths files.

These files are generated and used to create the index pack sent to the Xrefs service.
They should not be included in the tar ball with source files.

BUG= 673462 

Change-Id: I134144b5e18fb314715b247f531b8911bae0da66
Reviewed-on: https://chromium-review.googlesource.com/419018
Commit-Queue: Emma Söderberg <emso@chromium.org>
Commit-Queue: Dave Sansome <dsansome@chromium.org>
Reviewed-by: Dave Sansome <dsansome@chromium.org>

[modify] https://crrev.com/691add00f8f9ba2813e1b3a02bb98c41a38c6556/scripts/slave/archive_source_codesearch.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build.git/+/fd30e6d4d3755bddbb81e675531f97db12e27e75

commit fd30e6d4d3755bddbb81e675531f97db12e27e75
Author: Emma Soederberg <emso@chromium.org>
Date: Tue Dec 13 08:57:42 2016

Updates comments to include info about .filepaths filtering.

BUG= 673462 

Change-Id: Id0c0d6395be4859b7d1293dea4d230c8c57c4a44
Reviewed-on: https://chromium-review.googlesource.com/418720
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Emma Söderberg <emso@chromium.org>

[modify] https://crrev.com/fd30e6d4d3755bddbb81e675531f97db12e27e75/scripts/slave/archive_source_codesearch.py