These tests are not hermetic, and use the actual Flutter SDK. While they don't require actual devices, they run flutter_tester to test Dart web debug services (dwds) and Flutter integration.
Use this command to run (from the flutter_tools directory):
../../bin/cache/dart-sdk/bin/dart run test test/web.shard
These tests are expensive to run and do not give meaningful coverage information for the flutter tool (since they are black-box tests that run the tool as a subprocess, rather than being unit tests). For this reason, they are in a separate shard when running on continuous integration and are not run when calculating coverage.