In case of PartitionAlloc project in Chromium, there is a case that
it's useful to declare 'noparent' in the DEPS due to the situation
that a sub directory is exported to a standalone git project.

//base/allocator/partition_allocator/ (sub directory) is exported to
https://chromium.googlesource.com/chromium/src/base/allocator/partition_allocator.git

Change-Id: Ic51b6cd3928002962f25620b4d8797bed7802d1e
Bug: chromium:1151236
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3802719Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Joanna Wang <jojwang@chromium.org>