[FFe] Bottom-edge gesture to open tabs list in the browser application

[Olivier Tilloy]

This bug is to request a feature freeze exception in order to land the work done to implement bottom-edge gesture commanded tabs view in webbrowser-app, on touch devices.

On desktop, the mechanism to open the list of open tabs remains unchanged (from the drawer menu), although the view itself has been revamped a bit to conform to the latest visual designs (and that affects both touch and desktop).

Note that this doesn’t affect at all the webapp container.

The relevant merge request is: https://code.launchpad.net/~osomon/webbrowser-app/bottom-edge/+merge/248019.
Although the diff is huge, most of it is code imported from lp:unity8 to leverage the DirectionalDragArea component, which is not available publicly in the UITK yet (but is being considered for inclusion). This imported code will eventually go away, I am actively lobbying to get it integrated in the UITK.

The feature itself has been in development for several months (since the beginning of the vivid cycle really, with many interruptions in between). I was hoping to land it before feature freeze, but it didn’t happen because of shuffled priorities.

The design specification is available at https://docs.google.com/a/canonical.com/presentation/d/1Qrd4Flfs3EH-fI79IfrYgLdAx2nce-L7ve8NKLCX324/edit#slide=id.g2acbd6553_031. This is a partial implementation only, agreed upon with design (the complete feature will land in several iterations).

[Steve Langasek (vorlon)]

Phone-specific functionality. FFe approved.