Back before I changed the way keyframe style was resolved (https://bugs.webkit.org/show_bug.cgi?id=20995), I needed to call styleSheetChanged() after deleting or inserting keyframe rules so the keyframe style could be recomputed. But this caused ALL style to be recomputed, which was really expensive and also required a complete redraw of the page. After the change it is no longer necessary to do the styleSheetChanged() call because RenderStyles are created as needed when the animation is started. removing this call will significantly improve performance of adding or removing keyframes.
Created attachment 24209 [details] Patch, including LayoutTest file
Comment on attachment 24209 [details] Patch, including LayoutTest file r=me
Will land.
My Mac Mini died in the middle of testing this patch. I'm going to take it into the store tomorrow.
We'll land this
Sending LayoutTests/ChangeLog Adding LayoutTests/css3/change-keyframes-expected.txt Adding LayoutTests/css3/change-keyframes.html Sending WebCore/ChangeLog Sending WebCore/css/WebKitCSSKeyframesRule.cpp Transmitting file data ..... Committed revision 37592.