[infra] Improve documentation of skip in dm_flags

I have trouble remembering how to interpret the skip
strings, so I documented it more and required the use of
four named arguments. Regex helped transform the old calls
into the new ones.

Change-Id: I2b970053b95b9a4d3d90a718b5790b0b25ce8dae
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/503736
Reviewed-by: Eric Boren <borenet@google.com>
1 file changed