The Dart SDK is downloaded from one of the supported channels,
cached in bin/cache/dart-sdk
and is used to run Flutter Dart code.
The file bin/internal/dart-sdk.version
determines the version of Dart SDK
that will be downloaded. Normally it points to the dev
channel (for example,
1.24.0-dev.6.7
), but it can also point to particular bleeding edge build
of Dart (for example, hash/c0617d20158955d99d6447036237fe2639ba088c
).