Implement PaintLayer::scrollsWithViewport for SPv2.

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

Index: third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
diff --git a/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2 b/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
index 3e96a43bbe3199d91bcef85c82a5475a96e1acf5..efc68708303d4e37f86d1f8bdb74b4aa5d88db06 100644
--- a/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
+++ b/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
@@ -246,6 +246,7 @@ Bug(none) compositing/layer-creation/fixed-position-out-of-view-with-backdrop-fi
 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 ]
@@ -316,6 +317,9 @@ Bug(none) compositing/overflow/scroll-parent-with-non-stacking-context-composite
 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 ]