Updater Remove Quarantine Bit on Install for Mac

Currently, if the updater is installed via the browser on launch, when
the browser calls --install on the updater and the updater copies its
files over to the home directory, the browser will set a
com.apple.quarantine variable on the updater set by the browser. During
install, the updater calls itself as a service via XPC, and during this,
if the quarantine bit is not cleared, then the updater will prompt the
user with "This program has been downloaded from the internet, would you
like to open it". By removing the quarantine bit, it prevents the
updater from showing that dialog to end-users.

Bug: 1223236
Change-Id: I6fc154537acc0c19c43801e2c35772fef141c562
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2984222
Commit-Queue: Michael Chang <donchan@microsoft.com>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#902042}