WebLayer is a high level embedding API to support building a browser. While it's built on top of src/content, the expectation is that the API will hide the Content API. WebLayer is envisioned to include support for all the modern HTML5 and browser features (e.g. UI for permissions, autofill, safe browsing etc...).
Mailing list: weblayer-dev@chromium.org
Bug tracker: Internals>WebLayer