GitLab

This relands r532919 which was reverted in r533667

The original patch worked only in the initial case but the corrected
layer bounds were clobbered in
ScrollingCoordinator::ScrollableAreaScrollLayerDidChange. Even though
CompositedLayerMapping::UpdateScrollingLayerGeometry is always called
after this method, in ScrollingCoordinator the bounds are set directly
on the WebLayer. In CLM we set the bounds on a GraphicsLayer which
caches the size itself. It'll only update the WebLayer bounds if the
new size differs from the cached size. Thus, even though the bounds
were changed in ScrollingCoordinator, CLM would early out since it
the GraphicsLayer size hasn't changed.

This CL applies the same fix in ScrollingCoordinator and also adds a
new test that covers the linked bug more end-to-end.

The original patch is uploaded in patchset 1 for easy diff'ing.

Bug: 801381
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I28f7088ef6b429875c6c984c45fd1c53cf813c02
Reviewed-on: https://chromium-review.googlesource.com/897962Reviewed-by: Tien-Ren Chen <trchen@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533913}