1848376 - Consider removing apz.allow_immediate_handoff pref

Status: NEW

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

Description

[Gregory Pappas [:gregp]]

According to bug 1528775 comment 6:

• The code that governs this behaviour was originally written for B2G, where we needed the "immediate handoff" behaviour due to the way B2G's hiding URL bar worked.
• Later that code was ported to all platforms, so all platforms inherited this behaviour.
• In bug 1230552, we changed the behaviour on Android in response to UX feedback, but left other platforms (B2G and desktop) alone.
• Then B2G was cancelled, leaving desktop the only platform with the "immediate handoff" behaviour.

Then, it was disabled on desktop as well, leaving no platform with this behavior. Should the pref be removed?

Comment 1

[Botond Ballo [:botond]]

I haven't come across any bug reports asking for immediate handoff behaviour or any mention of users having flipped this pref, so from a user impact point of view, I have no objection to removing this pref.

We do have some gtests that flip this pref; they're not necessarily tests for the immediate handoff behaviour, they just rely on immediate handoff behaviour to set up the scenario they want to test. To avoid losing test coverage, these tests should be revised to set up the relevant scenarios without relying on immediate handoff, rather than being removed.

Comment 2

[Botond Ballo [:botond]]

(In reply to Botond Ballo [:botond] from comment #1)

We do have some gtests that flip this pref; they're not necessarily tests for the immediate handoff behaviour, they just rely on immediate handoff behaviour to set up the scenario they want to test. To avoid losing test coverage, these tests should be revised to set up the relevant scenarios without relying on immediate handoff, rather than being removed.

A subset of these tests which have Scrollgrab in their name fall into a special category: they are exercising the vestigial "scrollgrab" feature that was used to implement the B2G dynamic toolbar.

The scrollgrab feature only works with immediate handoff, and so these tests cannot be revised to not rely on immediate handoff. Instead, we should just remove the vestiges of the scrollgrab feature, and the scrollgrab tests along with it.