Support overriding gclient config in a bot_update method

Bug: 713356
TBR=tandrii@chromium.org

Change-Id: I15d73492712b66c7670793f3c47e4cbd89d4e1cd
Reviewed-on: https://chromium-review.googlesource.com/484440Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>

recipes/recipe_modules/bot_update/api.py

@@ -357,21 +357,23 @@ class BotUpdateApi(recipe_api.RecipeApi):
 
   # TODO(machenbach): Replace usages of this method eventually by direct calls
   # to the manifest output.
-  def get_project_revision_properties(self, project_name):
+  def get_project_revision_properties(self, project_name, gclient_config=None):
     """Returns all property names used for storing the checked-out revision of
     a given project.
 
     Args:
       project_name (str): The name of a checked-out project as deps path, e.g.
           src or src/v8.
+      gclient_config: The gclient configuration to use. If omitted, the current
+          gclient configuration is used.
 
     Returns (list of str): All properties that'll hold the checked-out revision
         of the given project. An empty list if no such properties exist.
     """
+    cfg = gclient_config or self.m.gclient.c
     # Sort for determinism. We might have several properties for the same
     # project, e.g. got_revision and got_webrtc_revision.
-    rev_reverse_map = self.m.gclient.got_revision_reverse_mapping(
-        self.m.gclient.c)
+    rev_reverse_map = self.m.gclient.got_revision_reverse_mapping(cfg)
     return sorted(
         prop
         for prop, project in rev_reverse_map.iteritems()