flutter/bin/internal/README.md

Dart SDK dependency

The bin/internal/engine.version file controls which version of the Flutter engine to use. The file contains the commit hash of a commit in the https://github.com/flutter/engine repository. That hash must have successfully been compiled on https://build.chromium.org/p/client.flutter/ and had its artifacts (the binaries that run on Android and iOS, the compiler, etc) successfully uploaded to Google Cloud Storage.