Fix failure to pickle. Followup to CL:57682.

In the following example, cbuildbot failed with "can't pickle generator
objects" error in the CommitQueueCompletion stage:

http://chromegw/i/chromeos/builders/peach_pit%20paladin/builds/882

We fix this by converting the generator objects into the appropriate
Python datastructures. This was already being done previously but it
wasn't documented. Do this again, but add appropriate documentation.

BUG=chromium:240798
TEST=unit tests
Change-Id: I046792998a799bcb68e2a221db0eea3fff51a3da
Reviewed-on: https://gerrit.chromium.org/gerrit/57992
Reviewed-by: Ryan Cui <rcui@chromium.org>
Commit-Queue: David James <davidjames@chromium.org>
Tested-by: David James <davidjames@chromium.org>
1 file changed