GitLab

This is a reland of c54a52fa with the
native messaging host registered as user-level in the test, avoiding
issues where overriding the local machine registry to register the host
as system-level would cause renderer launching to fail on Windows 7.

Original change's description:
> Allow background mode while an extension is communicating with a native app.
>
> Add support for enabling background mode while an extension capable of
> accepting inbound native messaging launch requests is active. Allow
> cooperating native apps to launch Chrome without a browser window when
> initiating communications with a cooperating extension.
>
> Bug: 967262
> Change-Id: I61353c0becb341ad3e08a5a8635e171f9f9bd59b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898894
> Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
> Reviewed-by: Drew Wilson <atwilson@chromium.org>
> Reviewed-by: Tommy Martino <tmartino@chromium.org>
> Reviewed-by: Sergei Datsenko <dats@chromium.org>
> Commit-Queue: Sam McNally <sammc@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#716480}

Bug: 967262
Tbr: sergeyu@chromium.org, atwilson@chromium.org, tmartino@chromium.org, dats@chromium.org
Change-Id: Ice54f4f309c5714d3011647d845d7c2af9a1ed39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1923870Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720177}