Created attachment 300094 [details]
Scrolling iframes, doesn't redraw their content, unless you select some content inside it. I'm attaching a test case (open a test.html and try to scroll any of the iframes there).
I forget to mention that forcing the AC fixes it.
Created attachment 300105 [details]
Comment on attachment 300105 [details]
Clearing flags on attachment: 300105
Committed r211367: <http://trac.webkit.org/changeset/211367>
All reviewed patches have been landed. Closing bug.