This is only for development workflows.

(1) Build and run the chrome_sandbox
(2) Notice the solid grey wallpaper
(3) Right click on the wallpaper, Set Wallpaper
(4) Choose a wallpaper, notice the change
(5) Close the wallpaper picker window

What is the expected result?

The picked wallpaper should remain. And presumably should remain across sessions even for a stub user, since the shelf prefs (pinned apps, etc.) is preserved in the profile directory.

What happens instead?

The wallpaper goes back to grey as soon as the window is closed