Add skia_buildbot config

Goal is to eventually add a presubmit trybot for skia_buildbot
repository.
Similar to one that was added in
https://codereview.chromium.org/1141583002

Bug: skia:7049
Change-Id: I95a8e2b452a44a50dc177d520af4ce95129db6da
Reviewed-on: https://chromium-review.googlesource.com/671410Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Ravi Mistry <rmistry@chromium.org>

recipes/recipe_modules/gclient/config.py

@@ -174,6 +174,14 @@ def skia(c):  # pragma: no cover
   m = c.got_revision_mapping
   m['skia'] = 'got_revision'
 
+@config_ctx()
+def skia_buildbot(c):  # pragma: no cover
+  s = c.solutions.add()
+  s.name = 'skia_buildbot'
+  s.url = 'https://skia.googlesource.com/buildbot.git'
+  m = c.got_revision_mapping
+  m['skia_buildbot'] = 'got_revision'
+
 @config_ctx()
 def chrome_golo(c):  # pragma: no cover
   s = c.solutions.add()