We recommend most clients track our tip-of-tree as we work hard to keep it green. Doing so gives us timely feedback, and users the best chance of getting fixes.
If you require less frequent updates, we cut a stable milestone every four weeks along with Chrome.
Chromium (and Skia) have a staged branching strategy. Every four weeks a branch is cut from a relatively stable revision near HEAD, is stabilized for six weeks, and then promoted to stable.
Skia branches alongside Chromium, and progresses through the branch testing pipeline along with other Chromium components. The Chromium release process is thoroughly documented in the Chrome Release Cycle.
The branch/release dates are in the schedule. The current branches are listed in https://chromiumdash.appspot.com/branches.
Skia release notes for all milestones can be found in the Skia Graphics Release Notes.