Set rebaseline bot name/email in chromium repo via git config.

scripts/slave/recipes/infra/rebaseline_o_matic.expected/rebaseline_o_matic.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.infra.cron",
       "--builder",
       "rebaseline-o-matic",
@@ skipping 81 matching lines @@
       "@@@SET_BUILD_PROPERTY@got_v8_revision@\"801ada225ddc271c132c3a35f03975671d43e399\"@@@",
       "@@@SET_BUILD_PROPERTY@got_v8_revision_cp@\"refs/heads/master@{#43426}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_swarming_client_revision_cp@\"refs/heads/master@{#276089}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_webrtc_revision_cp@\"refs/heads/master@{#120644}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#170242}\"@@@",
       "@@@SET_BUILD_PROPERTY@got_angle_revision_cp@\"refs/heads/master@{#297276}\"@@@"
     ]
   },
   {
     "cmd": [
+      "git",
+      "config",
+      "user.name",
+      "Rebaseline Bot"
+    ],
+    "cwd": "[SLAVE_BUILD]/src",
+    "name": "git config"
+  },
+  {
+    "cmd": [
+      "git",
+      "config",
+      "user.email",
+      "blink-rebaseline-bot@chromium.org"
+    ],
+    "cwd": "[SLAVE_BUILD]/src",
+    "name": "git config (2)"
+  },
+  {
+    "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/src/third_party/WebKit/Tools/Scripts/webkit-patch",
       "auto-rebaseline",
       "--verbose",
       "--auth-refresh-token-json",
-      "/creds/refresh_tokens/blink_rebaseline_bot_rietveld",
-      "--commit-author",
-      "Rebaseline Bot <blink-rebaseline-bot@chromium.org>"
+      "/creds/refresh_tokens/blink_rebaseline_bot_rietveld"
     ],
     "cwd": "[SLAVE_BUILD]/src/third_party/WebKit",
     "name": "webkit-patch auto-rebaseline"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]