JSON check may be useful for files that don't necessaraly end with
.json. For example, infra/config/recipes.cfg should be a json file. This
change allows users to add custom file_filter that can include such
files.

R=apolito@google.com

Bug: 1223923
Change-Id: Ia6fc7f86fa368510baaee978d9a0a27eccb6b31f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2992735Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>