In WebKit2 on Windows, accelerated compositing happens on the main thread. This means that pauses on the main thread can result in stuttering animation (e.g., bug 57956).
We should move compositing off the main thread so that it isn't affected by the business of the main thread. This is how accelerated compositing works in WebKit1, and on Mac.
*** Bug 57956 has been marked as a duplicate of this bug. ***
This will be fixed by the fix for bug 58054.
*** This bug has been marked as a duplicate of bug 58054 ***