In general, for a normal `BoxFragment`, a `ExternalScrollId` is created
by directly using the `OpaqueNode::id` which is the heap address of the
`Node`. But for a `BoxFragment` from a `::before` or `::after` pseudo
element, we are using the next unused id (starting from zero) with an
increment of two.
This patch modifies so that we are using the bitwise or of
`OpaqueNode::id` and `FragmentType` as the `ExternalScrollId`. With
these changes, the `ExternalScrollId` for the pseudo elements would
remain the same after reflow (instead of getting a new scroll id).
Testing: New WPT test
Fixes: #43308
---------
Signed-off-by: Jo Steven Novaryo <steven.novaryo@gmail.com>
01689d241a