cbuildbot: plumb cbb_build_packages flag

Plumb the --cbb_build_packages flag that will be passed
to postsubmit builders inside of the --cbb_extra_args
to trigger postsubmit to only build the requested packages.

BUG=chromium:904156
TEST=local cbuildbot postsubmit tryjob and unittests

Change-Id: I86c2a0ba04deee837f48f153b9e60753b1bcdf81
Reviewed-on: https://chromium-review.googlesource.com/1447864
Commit-Ready: Gregory Meinke <gmeinke@chromium.org>
Tested-by: Gregory Meinke <gmeinke@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 789e35a..4f0f0fa 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -221,7 +221,7 @@
 
 
 class CustomParser(commandline.FilteringParser):
-  """Custom option parser which supports arguments passed-trhough to trybot"""
+  """Custom option parser which supports arguments passed-through to trybot"""
 
   DEFAULT_OPTION_CLASS = CustomOption
 
@@ -483,6 +483,12 @@
                           help='Run the build as a sanity check build.')
   group.add_remote_option('--debug-cidb', action='store_true', default=False,
                           help='Force Debug CIDB to be used.')
+  # cbuildbot ChromeOS Findit options
+  group.add_remote_option('--cbb_build_packages', action='split_extend',
+                          dest='cbb_build_packages',
+                          default=[],
+                          help='Specify an explicit list of packages to build '
+                               'for integration with Findit.')
 
   parser.add_argument_group(group)