libchrome: add base/functional/* headers

For forward compatibility with r1093705 libchrome where
base/{bind.h, callback.h, callback_forward.h, callback_helpers.h} are
moved to base/functional/.
This makes migration in CrOS easier on client packages shared with
Android.

Bug: 266161904
Test: presubmit
Change-Id: I7622eb821d5a7b97f37a725b0b860cebd0e99e9a
4 files changed