Implement PaintLayer::scrollsWithViewport for SPv2.

third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2

 # Expectations for slimming paint v2
 # See: https://docs.google.com/document/d/1QCM912Dr6u38DqyQqd7pxQxDy8FFOoWMMDq7uAXqKdA/view
 # We are focused on fast/, compositing/, and svg/ with all other directories skipped (for now).
 
 Bug(none) accessibility/ [ Skip ]
 Bug(none) animations/ [ Skip ]
 Bug(none) app_banner/ [ Skip ]
 Bug(none) battery-status/ [ Skip ]
 Bug(none) bindings/ [ Skip ]
 Bug(none) bluetooth/ [ Skip ]
@@ skipping 228 matching lines @@
 Bug(none) compositing/layer-creation/fixed-position-nonscrollable-iframes-in-scrollable-page.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view-dynamic.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view-positioning.html [ Crash Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view-scaled-scroll.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view-scaled.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view-scroll-reason.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view-with-backdrop-filter.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-out-of-view.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-scroll.html [ Failure ]
 Bug(none) compositing/layer-creation/fixed-position-under-transform.html [ Failure ]
+crbug.com/671838 compositing/layer-creation/iframe-background-attachment-fixed.html [ Failure ]

[chrishtr, 2016/12/06 23:56:07]

This was an existing bug exposed by removing SPv2-incompatible scrolling update
code in FrameView.

 Bug(none) compositing/layer-creation/no-compositing-for-fixed-position-under-transform.html [ Failure ]
 Bug(none) compositing/layer-creation/no-compositing-for-preserve-3d.html [ Failure ]
 Bug(none) compositing/layer-creation/overflow-scroll-overlap.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-animation-clipping.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-animation-container.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-animation.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-child-layer.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-clipping.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-transformed-3d.html [ Failure ]
 Bug(none) compositing/layer-creation/overlap-transformed-and-clipped.html [ Failure ]
@@ skipping 50 matching lines @@
 Bug(none) compositing/overflow/reparented-scrollbars-non-sc-anc.html [ Failure ]
 Bug(none) compositing/overflow/resize-painting.html [ Failure ]
 Bug(none) compositing/overflow/scaled-overflow.html [ Failure ]
 Bug(none) compositing/overflow/scroll-ancestor-update.html [ Failure ]
 Bug(none) compositing/overflow/scroll-parent-absolute-with-backdrop-filter.html [ Failure ]
 Bug(none) compositing/overflow/scroll-parent-absolute.html [ Failure ]
 Bug(none) compositing/overflow/scroll-parent-with-non-stacking-context-composited-ancestor.html [ Failure ]
 Bug(none) compositing/overflow/scrollbar-layer-placement.html [ Failure ]
 Bug(none) compositing/overflow/scroller-with-border-radius.html [ Failure ]
 Bug(none) compositing/overflow/scrolling-content-clip-to-viewport.html [ Failure ]
+crbug.com/667946 compositing/overflow/scrolls-with-respect-to-nested.html [ Failure ]

[chrishtr, 2016/12/06 23:56:07]

These are broken because viewport scrolling in general is not yet working for
SPv2,
so we can't detect that a fixed-position element doesn't scroll w.r.t. the
viewport.

+crbug.com/667946 compositing/overflow/scrolls-with-respect-to-transform.html [ Failure ]
+crbug.com/667946 compositing/overflow/scrolls-with-respect-to.html [ Failure ]
 Bug(none) compositing/overflow/textarea-scroll-touch.html [ Failure ]
 Bug(none) compositing/overflow/universal-accelerated-overflow-scroll.html [ Failure ]
 Bug(none) compositing/overlap-blending/children-opacity-huge.html [ Failure ]
 Bug(none) compositing/overlap-blending/reflection-opacity-huge.html [ Failure ]
 Bug(none) compositing/perpendicular-layer-sorting.html [ Failure ]
 Bug(none) compositing/plugins/webplugin-reflection.html [ Failure ]
 Bug(none) compositing/reflections/animation-inside-reflection.html [ Failure ]
 Bug(none) compositing/reflections/compositing-change-inside-reflection.html [ Failure ]
 Bug(none) compositing/reflections/deeply-nested-reflections.html [ Failure ]
 Bug(none) compositing/reflections/load-video-in-reflection.html [ Failure ]
@@ skipping 1834 matching lines @@
 # fast/forms/search/search-vertical-alignment.html
 # fast/forms/search/searchfield-heights.html
 # fast/forms/text/text-font-height-mismatch.html
 # fast/forms/text/textfield-overflow-by-value-update.html
 # fast/replaced/width100percent-searchfield.html
 #
 # SPv2 correctly positions a background clip that includes the transformed size of div #two.
 # SPv1 does not understand how to apply transforms properly in PaintLayerClipper (the issue is
 # also tracked in crbug.com/548184).
 # transforms/transform-overflow.html