You can try the field-trail extension until July of 2019 (contact me if you like to extent the field trails).
You can try the full extension for 30 days.
Currently, this extension is only tested on hosted and self-hosted Linux Ubuntu 16.04 and 18.04 x64 operating systems (including Hosted Ubuntu 1604 provided in Azure DevOps agent pool) and limited tested on VS2017 and Windows containers.
How to use this extension:
By default, the extension is using DART-SDK version 2.1.0.
You can change the version (see supported versions here); some examples are: 2.0.0 2.0.0-dev.54.0 1.24.3 220.127.116.11_r30798
On a self-hosted build agent, it would preserve the SDK toolkit; This would speed up the build for sequential builds, as it doesn't need download the took kit again. To disable use false instead of true.
Allows you to specify the build steps. Each build step must be delimited with a ;.
By default, the extension is using: dart --version; pub cache repair; pub get; pub global activate webdev; pub global run webdev build --output=web:build.
Those could be used for building DART web applications using pub.
dart --version will display the dart version number for this build.
pub cache repair will clean-up the listed dependencies in your pubspec.yaml file.
pub get will update or get the listed dependencies in your pubspec.yaml file.
pub global activate webdev will activate webdev.
pub global run webdev build --output=web:build will build the project.
*NOTE: each build step must be separated by a ;