WebRTC: Prepare for enabling bot_update for standalone recipe.

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_win_x64_rel.json

 [
   {
     "cmd": [
       "python",
       "-u",
+      "[BUILD]\\scripts\\slave\\bot_update.py",
+      "--master",
+      "tryserver.webrtc",
+      "--builder",
+      "win_x64_rel",
+      "--slave",
+      "slavename",
+      "--spec",
+      "cache_dir = None\nsolutions = [{'custom_vars': {'root_dir': 'src'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/webrtc/trunk'}, {'custom_vars': {'root_dir': 'src'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'webrtc-limited', 'url': 'svn://svn-mirror.golo.chromium.org/chrome-internal/trunk/webrtc-limited'}]",
+      "--revision_mapping_file",
+      "{\"src\": \"got_revision\"}",
+      "--issue",
+      "666666",
+      "--patchset",
+      "1",
+      "--output_json",
+      "/path/to/tmp/json",
+      "--revision",
+      "src@12345"
+    ],
+    "name": "bot_update",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@json.output@{@@@",
+      "@@@STEP_LOG_LINE@json.output@  \"did_run\": false, @@@",
+      "@@@STEP_LOG_LINE@json.output@  \"patch_failure\": false@@@",
+      "@@@STEP_LOG_LINE@json.output@}@@@",
+      "@@@STEP_LOG_END@json.output@@@"
+    ]
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
       "[DEPOT_TOOLS]\\gclient.py",
       "config",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'root_dir': 'src'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/webrtc/trunk'}, {'custom_vars': {'root_dir': 'src'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'webrtc-limited', 'url': 'svn://svn-mirror.golo.chromium.org/chrome-internal/trunk/webrtc-limited'}]"
     ],
     "name": "gclient setup"
   },
   {
     "cmd": [
       "python",
@@ skipping 409 matching lines @@
       "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"win_x64_rel\", \"issue\": 666666, \"mastername\": \"tryserver.webrtc\", \"patchset\": 1, \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"rietveld\": \"https://fake.rietveld.url\", \"slavename\": \"slavename\"}",
       "--annotate=gtest",
       "--test-type=voice_engine_unittests",
       "--builder-name=win_x64_rel",
       "--slave-name=slavename",
       "voice_engine_unittests.exe"
     ],
     "name": "voice_engine_unittests"
   }
 ]