Promote fixed/sticky if they can be scrolled
In https://crrev.com/624999, fixed and sticky positioned elements were promoted if they stick to a scroller. This patch takes that further and promotes fixed and sticky elements if they stick to a scroller, even if the scroller is overflow: hidden. This will let us remove the kHasNonLayerViewportConstrainedObjects main thread scrolling reason in a followup, which is difficult to support with CompositeAfterPaint. It is possible to have scroll animations with overflow hidden, scroll-behavior: smooth, and the root scroller. This is expected to regress the ie_chalkboard benchmark which now gets layerized which requires a raster larger than the visible rect. Before this patch, only the visible rect would be re-rasterized because there were no layers. This situation should be rare and this patch should be a small progression overall because it reduces main thread scrolling reasons. Bug: 649096 Change-Id: I6b1b15584166ace3dcd9b40d8271b13fb12b6366 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2100113 Commit-Queue: Philip Rogers <pdr@chromium.org> Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org> Auto-Submit: Philip Rogers <pdr@chromium.org> Reviewed-by:Xianzhu Wang <wangxianzhu@chromium.org> Cr-Commit-Position: refs/heads/master@{#842312}
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