dart-sdk/build
..
config
linux
mac
sanitizers
toolchain
win
.gitignore
compiled_action.gni
copy_tree.gni
dart_host_sdk_toolchain.gni
detect_host_arch.py
executable_suffix.gni
gn_helpers.py
gn_run_binary.py
prebuilt_dart_sdk.gni
README.dart.md
vs_toolchain.py

This directory was taken from a snapshot of flutter/engine/src/build/.

The snapshot was taken with a recursive copy cp -R of the directory from the flutter repository.

The contents has now diverged significantly from Flutter, and is maintained independantly by the Dart team. It is used to support the GN build system.