Bug 111617

Robohornet Pro's Resize Columns test (which involves repeatedly forcing layout by calling offsetTop) spends 40% of its time in WebCore::AnimationController::getAnimatedStyleForRenderer (this also accounts for about 18% of the time for the entire set of Robhornet Pro tests); 2/3 of this is spent in PropertyWrapperAcceleratedTransform::blend. This is on the Mac port. A call to getAnimatedStyleForRenderer is made in RenderLayer::currentTransform only when we're running an accelerated transform. As an interesting consequence, disabling accelerated animations (by skipping the calls to addAnimation in RenderLayerBacking::startAnimation) significantly reduces the total time for Robohornet Pro on the Mac port (on my machine, it takes about 5.8 s with accelerated animations, and about 4.4 s with non-accelerated animations), though the animations of course get choppy. For the same reason, the chromium port hits a 16% regression in Robohornet Pro (e.g. http://crbug.com/178419) when it accelerates all animations (instead of the present state, where the chromium port only accelerates animations that are added to GraphicsLayers already in the layer tree).