manifest_package is now chrome_public_manifest_package.

Chromium change:

https://chromium.googlesource.com/chromium/src/+/5172118ff57bef7dd2864c9fe891db9c05f76a2b

commit 5172118ff57bef7dd2864c9fe891db9c05f76a2b
Author: Tibor Goldschwendt <tiborg@chromium.org>
Date:   Mon Jun 24 21:57:47 2019 +0000

    [build] Add ability to define manifest package in GN

    The build system will verify that the manifest packages match if you
    specify it in both GN and the manifest.

    Bug: 891996