Set layer scroll data from PaintArtifactCompositor
This is a followup to [1] and begins setting scroll data on cc::Layer from
Blink's PaintArtifactCompositor. Because there's a 1:1 mapping between
scroll property nodes and ScrollableAreas, a WebLayerScrollClient field
has been added to the scroll property node. This field is then used in
the paint artifact compositor to set cc::Layer's did scroll callback.
With this patch, simple pages can be compositor wheel-scrolled on Windows.
[1] https://codereview.chromium.org/2680953002
BUG=667946
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Review-Url: https://codereview.chromium.org/2698473006
Cr-Commit-Position: refs/heads/master@{#451481}
8 files changed
