Add new owners

Both emaxx@ and drcrash@ at this time ar the only people working on
this code and familiar with it. Other owners have moved on or are
not available, and we end up in reviews like for CL:1234373 where
upstream owners declare themselves incompetent to review.

BUG=None
TEST=None

Change-Id: I3913bc9692a2668bab599eb0f08fc11b8457adc6
Reviewed-on: https://chromium-review.googlesource.com/1237251Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Yves Arrouye <drcrash@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592974}

chrome/browser/chromeos/attestation/OWNERS

+emaxx@chromium.org
+drcrash@chromium.org
 dkrahn@chromium.org
 mnissler@chromium.org
 bartfab@chromium.org