Resource Timing details for 4xx and 5xx resources

Hello,

Currently, the way RT data is applied for 4xx and 5xx resources differ
significantly across browsers. On Firefox and IE (and possibly Edge), RT
data is fully available for 4xx and 5xx resources (assuming TAO applies).
However on Chrome, RT data is completely unavailable for 4xx and 5xx
resources. Two places where this is talked about are:

1. https://bugs.chromium.org/p/chromium/issues/detail?id=460879#c19
2. https://github.com/w3c/resource-timing/issues/12

In both places, it seems like there is an acknowledgement that 4xx and 5xx
resources behave the same as any other resource and so RT data should be
available.

The question I have is whether clarification of 4xx and 5xx resources is
part of the L3 milestones? If so, that might address Chrome's long standing
issue of not providing RT data for such resources.

Thanks,
Karthik.