This directory contains the hashes of tar.gz files uploaded to cloud storage.
Hooks in the DEPS files run "download_from_google_storage" to download these
tarfiles, and unpack them. These tar files contain a stable Dart SDK, which
is used to build the observatory and to run the test scripts.

The hooks use the --auto-platform feature, so that only the SDK for the
current platform (linux, macos, or windows) is downloaded. This requires
the subdirectories to have the special names "linux", "win", and "mac", which
the download script is hardcoded to recognize.

The linux SDK has two extra dart executables added to the bin directory.
'dart-arm' and 'dart-arm64' are executables compiled to run on
arm and arm64 (aarch64) processors, respectively. We are currently
using the 32-bit ia32 build as the default on linux, windows, and macos.
If we switch to the 64-bit build on linux, the snapshots will no longer be
portable to arm and arm64, and we will need to upload complete SDKs for each
processor architecture.

To upload new versions of these tar files, use the "upload_to_google_storage"
tool in depot_tools, and download the new stable SDKs from the dartlang.org
web page. The arm executables must be copied from the machines that
build them, and stripped. Because these SDKs are used for the presubmit
dartfmt check on changed files, they may need to be updated often when
dartfmt is changing rapidly.