http://trac.webkit.org/projects/webkit/changeset/27486 caused a layout regression at my bank's website.
It's a smaller credit union so to avoid the hassle of me debugging with my login along with someone, I have a convincing reduction which I will attach.
In the reduction, there is a green image that is a header, and a red image that is in the main content portion of the page.
The red image should be touching the green image, and they should be left aligned.
After 27486, if you shrink the window vertically to the point where scrollbars are needed and much of the red image is not on screen, the main content div jumps to the left instead of remaining left justified with the header div.
Resizing the window horizontally while in this state shifts how much the div is off.
Before 27485 and in Firefox, these images stay touching and left-justified to each other
Created attachment 17096 [details]
Reduction - HTML + 2 images
Both on the live site and in my reduction, RenderBlock.cpp:606 is hit.
Mitz thought this was very odd on IRC :)
Created attachment 17097 [details]
HTML + 2 images
Whoops, meant to attach screenshots. Coming up...
Created attachment 17098 [details]
Screenshots of correct layout and weird layout after horizontal resizing
Created attachment 17100 [details]
Flip the signs
That's what happens when I try to write new code instead of copying and pasting old, working code.
Comment on attachment 17100 [details]
Flip the signs
Landed in <http://trac.webkit.org/projects/webkit/changeset/27504>.
Definitely fixed. Thanks!