Since v0.21.3 OOUI features a 'pushPin' icon, RevisionSlider should make use of this standard icon.
It should be placed in a OOUI ToggleButtonWidget (example)
Adjustments needed:
- The style should be frameless, something that probably needs to be solved by CSS (there is a frameless button, but it is not a toggle-button)
- It seems that the icon is too big in standard configuration now, It should have (roughly) the same size as now: 26*26px for the button area, 16*16 for the pushpin.
Helpful Links:
https://doc.wikimedia.org/mediawiki-core/master/js/#!/api/OO.ui.ToggleButtonWidget
https://www.mediawiki.org/wiki/Manual:Extension.json/Schema
https://phabricator.wikimedia.org/source/mediawiki/browse/master/docs/extension.schema.v1.json
Info for the Hackathon 2018
If you are interested in working on this at the Wikimedia-Hackathon-2018 , @WMDE-Fisch can help you with any questions :-)