certain histograms are using

units="GetLastError"

in their definition.

this means that chirp can't analyze them as it doesn't know about buckets. This also means viewing them in timeline doesn't really work e.g. https://uma.googleplex.com/p/chrome/timeline_v2?sid=a7fa4371616f4d2fdf2700320b3ca4dc

We should add a new enum type with all the known GetlastError and change these to use enum= rather than units=.

This will also mean all the correct codes will be displayed on the timeline graph rather than just numbers.