Created attachment 179056 [details]
When resizing a region in the chain, text bounces 1-2 pixels in subsequent regions. See attached test.
To clarify repro:
1. Slowly resize the window so the middle region gets resized as well
2. Even though the resize delta is too small to have text swap regions, the content in the rightmost region bounces vertically with one or two pixels.
Works for me on today's nightly (r151543)
I'd rather have Andrei take another look at it before deciding it got fixed. He's the one that logged the bug and might have more info on it.
The problem is caused by sub-pixel layout (still reproduces in Canary) and as long as the sub-pixel layout code is still in WebKit (even if it's disabled in the Mac port), the bug should still be open.