1918834 - Investigate why APZ can receive a scroll update with an out of bounds destination

Status: NEW

(Core :: Panning and Zooming, defect, P3)

Description

[Botond Ballo [:botond]]

While working on bug 1916137, I discovered something suspicious about the test case in bug 1915006: while the scroll frame which gets overscrolled in that bug has a fairly small scrollable rect (something like 400 x 150), in the test case the APZC for the scroll frame receives a NotifyScrollUpdated call with a scroll update whose destination is far out of range, e.g. x=70000 or such.

That sounds like it shouldn't happen (the main thread should clamp the scroll update to the valid scroll range), so I'm filing this bug to investigate the test case further.