Allow a single trybot to mirror multiple waterfall bots.

scripts/slave/recipe_modules/chromium_tests/test_api.py

Index: scripts/slave/recipe_modules/chromium_tests/test_api.py
diff --git a/scripts/slave/recipe_modules/chromium_tests/test_api.py b/scripts/slave/recipe_modules/chromium_tests/test_api.py
index 31490d760ec4707b9315ee3fee30b7947023d93a..a8ec511107db699212a63df70669e4e4e1278407 100644
--- a/scripts/slave/recipe_modules/chromium_tests/test_api.py
+++ b/scripts/slave/recipe_modules/chromium_tests/test_api.py
@@ -24,3 +24,9 @@ class ChromiumTestsApi(recipe_test_api.RecipeTestApi):
         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