Use LIKELY and UNLIKELY macros to wrap error generation. BUG=609673 Change-Id: I247f561712e30aa10bad77fabf614501d596915e Reviewed-on: https://chromium-review.googlesource.com/1021995 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>