Allow a single trybot to mirror multiple waterfall bots.

scripts/slave/recipe_modules/chromium_tests/test_api.py

 # Copyright 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.
 
 from recipe_engine import recipe_test_api
 
 from . import builders
 from . import trybots
 
 
 class ChromiumTestsApi(recipe_test_api.RecipeTestApi):
   @property
   def builders(self):
     return builders.BUILDERS
 
   @property
   def trybots(self):
     return trybots.TRYBOTS
 
   def platform(self, mastername, buildername):
     bot_config = builders.BUILDERS[mastername]['builders'][buildername]
     # TODO(phajdan.jr): Get the bitness from actual config for that bot.
     return self.m.platform(
         bot_config['testing']['platform'],
         bot_config.get(
             'chromium_config_kwargs', {}).get('TARGET_BITS', 64))
+
+  def normalize_bot_descs(self, bot_descs):
+    # Must have the same effect as normalize_bot_descs in the real API.
+    if not isinstance(bot_descs, (list, tuple)):
+      return [bot_descs]
+    return bot_descs