[Merge] lp:~ahayzen/webbrowser-app/dnd-tabs-001 into lp:webbrowser-app

[Bill Filler]

tested, works great!
One comment: if you create a private window and then some tabs, not sure if you should be able to drag that tab into a non-private window. Seems to be allowed in this implementation but not sure we want that behavior. Seems in Chromium you can only move private tabs between private windows and public tabs between public windows. Guessing we should follow same thing.
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https://code.launchpad.net/~ahayzen/webbrowser-app/dnd-tabs-001/+merge/307061
Your team Ubuntu Phablet Team is requested to review the proposed merge of lp:~ahayzen/webbrowser-app/dnd-tabs-001 into lp:webbrowser-app.