A handful of other areas are configured using Starlark in chromium. This particular use is in a very different capacity than Bazel - the Bazel equivalent in chromium is GN, and I have not seen any signs that GN will be replaced any time soon.
GN at least used to generate Ninja files. So I suppose now it will be generating Siso files?
edit: asked and answered, Siso is a "drop-in" replacement for Ninja, so presumably it can read .ninja files, and so GN probably didn't need to change much to accommodate it.