Repro for crbug.com/1189192

This tests that DevTools text editor viewport doesn't scroll unnecessarily when stepping.

Steps

1. Open DevTools
2. Reload the page and wait for DevTools to pause on crbug-1189192.js line 64
3. Press F10 or click on Step over next function
4. DevTools should step to line 65 and the viewport of the text editor should not move