WebRTC: Prepare for enabling bot_update for standalone recipe.

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

 [
   {
     "cmd": [
       "python",
       "-u",
+      "[BUILD]/scripts/slave/bot_update.py",
+      "--master",
+      "client.webrtc",
+      "--builder",
+      "Android Builder",
+      "--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'}]\ntarget_os = ['android']",
+      "--revision_mapping_file",
+      "{\"src\": \"got_revision\"}",
+      "--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'}]\ntarget_os = ['android']"
     ],
     "name": "gclient setup"
   },
   {
     "cmd": [
       "python",
@@ skipping 70 matching lines @@
       "--build_revision",
       "170242",
       "--factory-properties",
       "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"Android Builder\", \"mastername\": \"client.webrtc\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"slavename\": \"slavename\"}",
       "--build-properties",
       "{\"BUILD_CONFIG\": \"Release\", \"buildername\": \"Android Builder\", \"mastername\": \"client.webrtc\", \"recipe\": \"webrtc/standalone\", \"revision\": \"12345\", \"slavename\": \"slavename\"}"
     ],
     "name": "package build"
   }
 ]