Currently the debug protocol has no way for a debug adapter to request that the IDE open up a web browser. Some debug adapters, such as the C# debug adapter, can start a web browser as part of launching a web server project. The debug adapter needs some control to be able to signal when the web server is ready.

This could either be designed as an event (ex: WebServerReady) or as a callback request like starting processes in the terminal.

Dependent issue: dotnet/vscode-csharp#2657
Related issue: microsoft/vscode-debugadapter-node#153