metrics: Update to build against libchrome-271506

BUG=chromium:375032
TEST=`FEATURES=test emerge-$BOARD platform2`
TEST=Trybot runs on paladin, release, and chromiumos-sdk builders.

Change-Id: Icb524d3fd4001ebc36edc84306ea70db70f7599b
Reviewed-on: https://chromium-review.googlesource.com/200519


Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
Reviewed-by: Daniel Erat <derat@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>