Keep scroll by keyboard after child focused node is removed

So far, scroll stops if focused child node is removed
while scrolling parent node.
This is because the event handler passes the |MousePressNode|.
If focused child node(|MousePressNode|) is removed,
it will be null and scrollable area changed to document.

|LogicalScroll| finds scrollable area from |MousePressNode|.
If we save this scrollable area node,
we can get one more chance to find proper node to scroll.


Bug: 493078
Change-Id: I6e81ca0a0d15e0def66c8457840ca9e1343e8dba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611620
Commit-Queue: Lan Wei <lanwei@chromium.org>
Reviewed-by: Lan Wei <lanwei@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663040}
5 files changed