1350567 - On navigation to another SHEntry, we ought to recollect the previously current SHEntry as well to catch the LayoutHistoryState

Status: NEW

(Firefox :: Session Restore, enhancement)

Description

[Jan Henning [:JanH]]

Partial session store data updates on Desktop attempt to only collect any new entries that have been added while skipping anything older. History navigation (GoBack/Forward/GotoIndex) currently doesn't collect anything at all and just updates the current index. DOMTitleChanged currently still triggers a full collect, but with the advent of GroupedSHistory, even a full collect will only collect data within the current process and will not update any older previous data living in another process.

This is a problem if we want to reliably save the LayoutHistoryState (i.e. session history scroll positions etc.), because the LayoutHistoryState is only updated when navigating *away* from a session history entry.

This means that for any of OnHistoryGoBack/GoForward/GotoIndex (or simply OnIndexChanged), just refreshing the current history index is no longer enough - we need to re-collect the SHEntry of the previously current history index as well.
Likewise, for OnHistoryNewEntry, just getting the new entry no longer suffices - the previous SHEntry needs to be collected again as well.

Unfortunately, GroupedSHistory poses an obstacle here, because the previous SHEntry might live in a different process, which complicates retrieving its data again.

Comment 1

[Florian Quèze [:florian]]

Not sure why this was tagged fxperf, seems to be mostly a correctness issue.

Comment 2

[Jan Henning [:JanH]]

It is a hard blocker for bug 1350569, which in turn definitively is a performance issue (although no idea how large).