when you want to see what changed between two versions, gitiles can be used to view two versions for src.git by hand like:
https://chromium.googlesource.com/chromium/src/+log/69.0.3497.21..69.0.3497.22

ignoring that's kind of a pita to come up with by itself, it only shows changes in the src.git repo.  it'd be nice if we had a tool that also walked the repos that got rolled ... for example, that delta shows that libvpx got updated, but listing those commits requires more manual work (going to the respective repo, loading up the list of commits in there by hand, etc...).

crosland/ has a UI where you can type in two CrOS versions and it'll find all the repos with changes and show them to you.