Created attachment 236109 [details]
This did not happen as of yesterday on trunk. It's reproducible on my machine, at least.
1. Go to a website (eg., http://www.nihilogic.dk/labs/tetris/)
2. Set breakpoint (eg., tetris.js:95)
3. Hit the breakpoint (eg., press any key)
The regression was introduced in <http://trac.webkit.org/r172129> which is a mega merge commit. Proceeding with teasing out the individual merge revision that is the culprit.
The issue is due r170680: <http://trac.webkit.org/r170680> which was merged in r172129. Will roll out the patch for now while I figure out what the root issue is, and re-open https://bugs.webkit.org/show_bug.cgi?id=134420 to do the real work.
Patch for r170680 rolled out in r172372: <http://trac.webkit.org/r172372>.