In www.reddit.com, when clicking any link to the comments (those with name XXX comments, where XXX is a number), the data that arrives to the dispatchDecidePolicyForNavigationAction is incomplete: the action type is wrong, and the event associated with it lacks any data about button the key modifier keys pressed.
This was working in r42054, and I'd say it broke in the next commit by Darin (r42055), but I won't get to test it properly tonight.
I tried building the revision 42055 with the patch from 42069 (gtk+ build fix after 42055), and it doesn't work, indeed. I also tried revision 42054 with the patch from 42069, just to be sure it is not our fix that breaks it, and it works. So it seems like 42055 caused the problem, indeed.
Created attachment 29072 [details]
reduced test case
The problem seems to happen for links with target="_parent". I haven't bothered creating a page with actual framesets, but that may be a good thing to do for a layout test.
Created attachment 29076 [details]
Comment on attachment 29076 [details]