[metrics] Update metrics to build against libchrome-180609

base/eintr_wrapper.h moved to base/posix/eintr_wrapper.h

CQ-DEPEND=Ib19c1382ab28ae7632728aa672478da2feb3950e

BUG=chromium-os:38941
TEST=emerge the metrics package with tests enabled.
STATUS=Fixed

Change-Id: I5d72d8934930ce394786ee151fd8f390b5caf2e1
Reviewed-on: https://gerrit.chromium.org/gerrit/43297


Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
Commit-Queue: Chris Masone <cmasone@chromium.org>