(See crbug.com/549699 and  crbug.com/609385  for context)

a. Create the following repos in the chromium gerrit instance:

aosp/platform/external/libbrillo
aosp/platform/system/tpm

(there should be an "aosp" git repo in the chromium instance with a bunch of other repos).

b. Initialize the master branch on them with a one-time push from AOSP/master equivalent repo (not active mirroring of master, see below why). The corresponding AOSP repo is the same name but removing the "aosp/" prefix from the path.

c. Allow developers to upload CLs to these two repos for review, like any other chromium repo.