The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f8bebb7c76d17916a0306550287e15b687cfa656

commit f8bebb7c76d17916a0306550287e15b687cfa656
Author: Peter Beverloo <peter@chromium.org>
Date: Thu Aug 16 20:00:52 2018

Support the `silent` property for the chrome.notifications API

Native notification platforms use default (or configurable) indicators,
so if an extension wants to play their own notification sound they
should have the ability to mute those. This property already was
available for the Web Notification API.

Bug:  872698 
Change-Id: Ie183ec9b28ff5bb80c674cc81b4cb275442aac0b
Reviewed-on: https://chromium-review.googlesource.com/1169050
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583782}
[modify] https://crrev.com/f8bebb7c76d17916a0306550287e15b687cfa656/chrome/browser/extensions/api/notifications/notifications_api.cc
[modify] https://crrev.com/f8bebb7c76d17916a0306550287e15b687cfa656/chrome/browser/extensions/api/notifications/notifications_apitest.cc
[modify] https://crrev.com/f8bebb7c76d17916a0306550287e15b687cfa656/chrome/common/extensions/api/notifications.idl
[modify] https://crrev.com/f8bebb7c76d17916a0306550287e15b687cfa656/chrome/test/data/extensions/api_test/notifications/api/partial_update/background.js