[Merge] lp:~fboucault/webbrowser-app/combo_box_better_ux into lp:webbrowser-app/staging

[Florian Boucault]

> In fact left/right arrow keys shouldn’t navigate at all. Just verified that
> they don’t in chromium on desktop.

Done
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https://code.launchpad.net/~fboucault/webbrowser-app/combo_box_better_ux/+merge/316571
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