Summary:
- Donut charts is same as pie chart with few extra options to control size of the hole and to show/hide a big total in it.
- Add a new option type to tune a numeric options using a slider/spinner/keyboard.
- Add a new option type to tune a numeric options using a slider/keyboard
- Add a new .propWithDefault method to ObjObservable to allows to set a default value when options is undefined.
- mocha-webdriver's findContent does not work to find content in svg elements. So had to tweak original function into a sister function using .textContent instead.
Test Plan: Adds new tests
Reviewers: dsagal
Reviewed By: dsagal
Subscribers: anaisconce, dsagal
Differential Revision: https://phab.getgrist.com/D3107
