nspr: upgraded packages to upstream

Upgraded dev-libs/nspr to version 4.12 on amd64, arm, x86

BUG=chromium:596217
TEST=build; CQ is happy
CQ-DEPEND=I6d76a10d332f57f4bd22fb6f55a761cf0237e837

Change-Id: I8bf3e3db02f81b135fa69b4a849549d53291f734
Previous-Reviewed-on: https://chromium-review.googlesource.com/333669
(cherry picked from commit f61cb497c4fb6429d281882e3e4b5e69e5c0d3a9)
Reviewed-on: https://chromium-review.googlesource.com/335202
Reviewed-by: Ryan Sleevi <rsleevi@chromium.org>
Commit-Queue: Ryan Sleevi <rsleevi@chromium.org>
Tested-by: Ryan Sleevi <rsleevi@chromium.org>
4 files changed