Hey,
the older dev tool in the browser is outdatet and closed.
All custom visuals are built over the pbiviz tool now.
Here is a link:
https://powerbi.microsoft.com/en-us/blog/power-bi-custom-visuals-developer-tools-hit-v1/
Iám not sure the old api is the same like the new one. But they promise us to update the api soon.
I saw the drilldown function in git as merge. Maybe that function is in the next version.
You can do Tooltips over svg with append text. But iam not sure that help you for your old visual.
I think we have a hard time in the moment.
Nice Regards
Mcburn