`git rev-parse --verify` works only on a local clone, I guess.  In gsubmodd we have only the root repo (however, I suppose once we convert to using gclient revinfo that wouldn't be true any more).

Maybe another alternative:

$ curl 'https://chromium.googlesource.com/chromium/blink/+/661b5d2?format=JSON'

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/a16248466a3a74f139ad55a4468f720c63b94cfd

commit a16248466a3a74f139ad55a4468f720c63b94cfd
Author: Alan Bram <flyboy@chromium.org>
Date: Fri Oct 05 19:58:44 2018

Look up abbreviated commit hashes via JSON ReST API.

Bug:  872846 
Change-Id: Ib1f460ae11a0afde2de6844d3d51022dcec9befa
Reviewed-on: https://chromium-review.googlesource.com/c/1256064
Commit-Queue: Alan Bram <flyboy@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Cr-Commit-Position: refs/heads/master@{#18116}
[modify] https://crrev.com/a16248466a3a74f139ad55a4468f720c63b94cfd/infra/libs/deps2submodules/deps2submodules.py
[add] https://crrev.com/a16248466a3a74f139ad55a4468f720c63b94cfd/infra/libs/deps2submodules/test/deps2submodules_test.expected/Deps2SubmodulesTest.testAbbreviatedCommitHash.json
[modify] https://crrev.com/a16248466a3a74f139ad55a4468f720c63b94cfd/infra/libs/deps2submodules/test/deps2submodules_test.py