When building the new SDK DAPs, this functionality was missed from the Flutter adapter (but added to the Dart CLI adapter).
As well as passing a VM Service URI directly, we support passing a file that can be polled for it.
This uses the same mechanism we use to obtain the VM Service URI from a Dart debug session (we run `dart --write-service-info=foo.json my_file.dart` and then poll that file which the VM will write) and is useful for users that have their own mechanism for launching an app (for example using custom Flutter embedders - see https://github.com/Dart-Code/Dart-Code/issues/3353) to provide a VM Service URI once the app is up and running.
Fixes https://github.com/Dart-Code/Dart-Code/issues/4577.
The editor is set to hot-reload-on-save by default so saving while the debug session is starting currently prints an error:
Failed to Hot Reload: app 'null' not found

This change skips the call to `app.restart` if the app hasn't started yet to avoid printing an error.
* [flutter_tools] Forward app.webLaunchUrl event from Flutter to DAP clients
Fixes https://github.com/Dart-Code/Dart-Code/issues/4292.
* Update packages/flutter_tools/lib/src/debug_adapters/flutter_adapter.dart
Co-authored-by: Christopher Fujino <fujino@google.com>
* Another static const instead of final
Co-authored-by: Christopher Fujino <fujino@google.com>
* [flutter_tools/dap] Add support for forwarding `flutter run --machine` requests to the DAP client
Currently the only request that Flutter sends to the client is `app.exposeUrl` though most of this code is generic to support other requests that may be added in future.
* Improve comment
* Fix thrown strings
* StateError -> DebugAdapterException
* Add a non-null assertion and assert
* Use DebugAdapterException to handle restartRequests sent before process starts
* Fix typo + use local var
* Don't try to actually send Flutter messages in tests because there's no process
* [flutter_tools] [dap] Ensure DAP sends app.stop/app.detach during terminate
Fixes an issue where the flutter_tester device may not be cleaned up correctly if we just terminate the Flutter process.
* Update integration test expectations
* Revert accidental commit
* [flutter_tools] [dap] Add support for passing env variables to spawned processes
* Use named args
* Use in-memory fs and FakePlatform
* Pass filesystem style to MemoryFileSystem
* Don't terminate Dart process pids from VM Service
These processes may be on another device, and in the case of attach the debugee should not be terminated anyway.