GitLab

This is a reland of c2dee48d

Original change's description:
> Add async X11 response handling
> 
> This CL adds x11::Future::OnResponse() to install a response handler
> for X11 requests.  Previously you could only Sync() to get the
> response.
> 
> ui::X11WorkspaceHandler is changed to demo usage of async response
> handling.  Eventually it should be migrated to a higher-level property
> handler, like we currently have in x11_util.* for Xlib.
> 
> R=sky
> CC=​msisov,nickdiego
> BUG=1066670
> 
> Change-Id: Ifcab2553008395bcfd9090e6aa1ccc5b4e53ae2e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2164245
> Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#763458}

Bug: 1066670
Change-Id: Ia1411c79d41a22e8747bc47a4e16616448f8ce0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2173152
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#764019}