Adding label and blocking on the already existing bug that tracks fuzzing coverage for metrics (which I wasn't aware of).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform2/+/94f83c546c179a6fa868a7e7ce486e52100d1ebd

commit 94f83c546c179a6fa868a7e7ce486e52100d1ebd
Author: Mattias Nissler <mnissler@chromium.org>
Date: Fri Nov 23 03:07:47 2018

metrics: Add fuzzer for serialization_utils parsing

Add a fuzzer to cover the metrics sample parsing.

BUG= chromium:906625 
TEST=Builds and passes tests.

Change-Id: Ibe708177121d41cea248c62e0dd66dcf266490c3
Reviewed-on: https://chromium-review.googlesource.com/1341793
Commit-Ready: Mattias Nissler <mnissler@chromium.org>
Tested-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Mattias Nissler <mnissler@chromium.org>

[modify] https://crrev.com/94f83c546c179a6fa868a7e7ce486e52100d1ebd/metrics/metrics.gyp
[add] https://crrev.com/94f83c546c179a6fa868a7e7ce486e52100d1ebd/metrics/serialization/metrics_serialization_utils_fuzzer_seed_corpus.zip
[add] https://crrev.com/94f83c546c179a6fa868a7e7ce486e52100d1ebd/metrics/serialization/metrics_serialization_utils_fuzzer.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/a6d80150b6aa41dd19114426fe1713085fc591cf

commit a6d80150b6aa41dd19114426fe1713085fc591cf
Author: Mattias Nissler <mnissler@chromium.org>
Date: Fri Nov 30 00:09:10 2018

chromeos-base/metrics: Install serialization_utils_fuzzer

BUG= chromium:906625 
TEST=Builds and installs fuzzer when requested.
CQ-DEPEND=CL:1341793

Change-Id: I1e34972772e58853d443d81ed4975db450162697
Reviewed-on: https://chromium-review.googlesource.com/1341795
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>

[modify] https://crrev.com/a6d80150b6aa41dd19114426fe1713085fc591cf/chromeos-base/metrics/metrics-9999.ebuild