bot_update: understand new Gerrit patch properties.

recipe_modules/tryserver/api.py

Index: recipe_modules/tryserver/api.py
diff --git a/recipe_modules/tryserver/api.py b/recipe_modules/tryserver/api.py
index f18c2b5d93227ffe0cf4c351de2dcf3b64dbfdb3..05aad08ab845673e9f6ef5d67f726191070f35e8 100644
--- a/recipe_modules/tryserver/api.py
+++ b/recipe_modules/tryserver/api.py
@@ -41,6 +41,9 @@ class TryserverApi(recipe_api.RecipeApi):
   @property
   def is_gerrit_issue(self):
     """Returns true iff the properties exist to match a Gerrit issue."""
+    if self.m.properties.get('patch_storage') == 'gerrit':
+      return True
+    # TODO(tandrii): remove this, once nobody is using buildbot Gerrit Poller.
     return ('event.patchSet.ref' in self.m.properties and
             'event.change.url' in self.m.properties and
             'event.change.id' in self.m.properties)