Improve docs on rebaseline git config user name/email override.

scripts/slave/recipes/infra/rebaseline_o_matic.py

 # Copyright (c) 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Generates new baselines for Blink layout tests that need rebaselining.
 
 Intended to be called periodically. Syncs to the Blink repo and runs
 'webkit-patch auto-rebaseline', which processes entries in
 LayoutTests/TestExpectations that are marked with 'NeedsRebaseline'.
 
@@ skipping 13 matching lines @@
 
 def RunSteps(api):
   RIETVELD_REFRESH_TOKEN = '/creds/refresh_tokens/blink_rebaseline_bot_rietveld'
 
   api.gclient.set_config('chromium')
   api.bot_update.ensure_checkout(force=True)
 
   cwd = api.path['checkout'].join('third_party', 'WebKit')
 
   # Changes should be committed and landed as the rebaseline bot role account.
+  # The base chromium repo setup configures chrome-bot@ as the author/committer.
+  # We could attempt use of command-line arguments to git commands to specify
+  # the rebaseline bot name/email, but in fact this is insufficient to override
+  # due to precedence. Environment variables would likely work per the man page
+  # for git-commit-tree, but would require changes through both the auto-
+  # rebaseline script and 'git cl land', with this bot as the only intended
+  # customer.
+  #
+  # Given all tradeoffs, setting the chromium repo's user name/email to the
+  # intended rebaseline bot parameters in a persistent manner is deemed a
+  # reasonable alternate approach.
   api.git('config', 'user.name', 'Rebaseline Bot')
   api.git('config', 'user.email', 'blink-rebaseline-bot@chromium.org')
 
   api.python('webkit-patch auto-rebaseline',
              cwd.join('Tools', 'Scripts', 'webkit-patch'),
              ['auto-rebaseline', '--verbose',
              '--auth-refresh-token-json', RIETVELD_REFRESH_TOKEN],
              cwd=cwd)
 
 
 def GenTests(api):
   yield (api.test('rebaseline_o_matic') +
          api.properties(mastername='chromium.infra.cron',
                         buildername='rebaseline-o-matic',
                         slavename='fake-slave'))