Merge 120750 - Fix scrollbar layers being misplaced with a clipped owner layer

Merge 120750 - Fix scrollbar layers being misplaced with a clipped owner layer
https://bugs.webkit.org/show_bug.cgi?id=89486

Reviewed by Simon Fraser.

Source/WebCore:

Scrollbar layers are positioned relative to their parent layer. If
that parent gets clipped, then that positioning becomes incorrect and
scrollbars get positioned relative to the clipped bounds instead of
the full bounds. Fix by not clipping in this case.

Test: compositing/overflow/scrollbars-with-clipped-owner.html

* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::shouldClipCompositedBounds):

LayoutTests:

* compositing/overflow/scrollbars-with-clipped-owner-expected.png: Added.
* compositing/overflow/scrollbars-with-clipped-owner-expected.txt: Added.
* compositing/overflow/scrollbars-with-clipped-owner.html: Added.


TBR=enne@google.com
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=120843