Dart的官方页面，只给了一个拼凑下载地址的说明，没有给出具体的链接，这里统一列出来好了
Mac平台
32位下载地址：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-macos-ia32-release.zip
64位下载地址：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-macos-x64-release.zip
文档地址：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/api-docs/dartdocs-gen-api.zip
Windows平台
32位：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-windows-ia32-release.zip
64位：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-windows-x64-release.zip
文档：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/api-docs/dartdocs-gen-api.zip
Linux平台
32位：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-linux-ia32-release.zip
64位： https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-linux-x64-release.zip
ARM V7
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-linux-arm-release.zip
ARMv8 (ARM64):
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/sdk/dartsdk-linux-arm64-release.zip
文档：
https://storage.googleapis.com/dart-archive/channels/stable/release/2.4.0/api-docs/dartdocs-gen-api.zip