Add superproject got_revisions.

(1) bot_update (http://shortn/_I814yt6r9U) will use got_revision_mapping
in these configs to create builder properties
{
'got_revision': <revision>
'got_revision_superroject': <revision>
}
(2)
recipe testing a change will use these configs to go from:
CL's project -> project's name in gclient solutions -> got_revision string
(e..g 'https...infra/infra_superproject' -> '.' -> 'got_revision_superproject'

(3) then use e.g. 'got_revision_superproject' to get the <revision> it should use from (1) and pass to wherever. in the presubmit recipes case, we're passing it as upstream to presubmit_support.py http://shortn/_BHBdN9p7ja

After this change we can add infra and internal presubmit tryjobs to the infra_superproject repo.

Recipe-Nontrivial-Roll: infra
Recipe-Nontrivial-Roll: chromiumos
Bug: 1415507
Change-Id: Ia9804325c35b6071afa73d1b1099695ea6ae0b03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4570829
Auto-Submit: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

recipes/recipe_modules/gclient/config.py

@@ -293,6 +293,7 @@ def infra_superproject(c):
   soln.name = '.'
   soln.url = 'https://chromium.googlesource.com/infra/infra_superproject.git'
   c.got_revision_mapping['infra'] = 'got_revision'
+  c.got_revision_mapping['.'] = 'got_revision_superproject'
   c.repo_path_map.update({
       'https://chromium.googlesource.com/infra/luci/gae':
       ('infra/go/src/go.chromium.org/gae', 'HEAD'),
@@ -313,6 +314,7 @@ def infra_internal_superproject(c):
   soln.custom_vars = {'checkout_internal': True}
   soln.url = 'https://chromium.googlesource.com/infra/infra_superproject.git'
   c.got_revision_mapping['infra_internal'] = 'got_revision'
+  c.got_revision_mapping['.'] = 'got_revision_superproject'
   c.repo_path_map.update({
       'https://chrome-internal.googlesource.com/infra/infra_internal':
       ('infra_internal', None)