Is this an existing API or one undergoing construction?

See the blocking bug. :) I don't have time to do this in the short term but I wanted to have the bug filed as I occasionally get into cases where this would be useful.

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot