Steps to reproduce:

1. Check out tip-of-tree flutter.
2. Edit //packages/flutter/test/material/about_test.dart to add while (true) on line 121 (just before a call to pumpWidget). This is just so that the test will run forever. The details don't matter.
3. Run flutter test --start-paused test/material/about_test.dart. It will print out a URL.
4. Open the given URL.
5. Click the "Isolate" link at the bottom.
6. Go to main > cpu profile at the top.
7. Click "Enable profiler".
8. Go to the debugger and run "continue".
9. Go back to the profiler and click Refresh. There are no samples.