platform2: Switch over to libchrome r323904

Using revision 323904 of libchrome by default. Fixed a few minor
compiler error due to a change in the new libchrome's headers.

BUG=chromium:472654
TEST=./build_packages
CQ-DEPEND=CL:264350

Change-Id: I0d57f34403f60c3d60d9159b60b498bf7ff166f3
Reviewed-on: https://chromium-review.googlesource.com/264311


Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>