Chromium's presubmits contain a lot of latent errors - presubmit errors
that will trigger the next time a file is modified, but have been
waiting for years. Flushing those out with "git cl presubmit --all"
works poorly because it exercises all presubmits simultaneously, which
is too slow and triggers too many failures. Adding a --files option lets
small areas of the tree or specific file types to be exercised in a
controlled manner.

Bug: 1311697
Change-Id: I36ec6a759a80000d6ed4a8cc218ece327d45f8d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3559174
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>