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This patch flips the PaintNonFastScrollableRegions flag to be enabled by
default. For more information about PaintNonFastScrollableRegions, see:
https://docs.google.com/document/d/1IyYJ6bVF7KZq96b_s5NrAzGtVoBXn_LQnya9y4yT3iw/view

The expectation has changed for compositor-touch-hit-rects-global.html
which is now correct and was incorrect due to https://crbug.com/992708.
The underlying bug has not been fixed.

Some expectations have new invalidations because going from scrollable
to non-scrollable (or vice versa) causes a scroll hit test display item
to disappear (or appear). paint/invalidation/resize-iframe-text.html and
paint/invalidation/compositing/iframe-inside-squashed-layer.html are
examples of tests changed due to this.

Some expectations have larger invalidations because the
resizer's scroll hit test display item uses the entire box as the
display item client. destroy-overlay-scrollbar.html and
destroy-scrollbar.html are examples of tests changed due to this.

Bug: 864567
Change-Id: Ia83de472ac2df10df09dd4476449dd6329848d11
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1734214Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688631}