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This issue is because we use a fixed transform to compute PositionInWidget
for each wheel or touchpad gesture event. If the OOPIF scrolled, use of the
fixed transform would give wrong coordinates.

In this patch, we recompute all scroll event's PositionInWidget in scroll
sequence.

This patch only changes wheel and touchpad gesture event. Touch and gesture
events be fixed in a fix in following patch.

Bug: 923560
Change-Id: I557d65e756f0933f2efbc26802179b3531c03826
Reviewed-on: https://chromium-review.googlesource.com/c/1427607Reviewed-by: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628228}