Example: https://chromiumdash.appspot.com/commit/580ffa0fb17bc4e924776eafd941bf1fab397cde

This is because Skia merges don't use standard format for merges / reverts on branch with a relevant branch & position, e.g. here's an example from a WebRTC merge:

Cr-Original-Commit-Position: refs/branch-heads/58@{#2}

Current logic (IIRC) parses for the @ in lines like that and uses it to determine branch / position, so since that's missing in Skia commits we're blind.

We could alternatively pass the branch in when evaluating commits in the first place (e.g. most commits are parsed by the cron jobs that automatically scrape trunk plus release branches) but that might leave us blind for builds pushed from non-standard branches.