1355244 - nsCSSFrameConstructor::ContentAppended should consistently null-check (or not-null-check) aContainer

Status: NEW

(Core :: Layout, enhancement, P3)

Description

[Daniel Holbert [:dholbert]]

nsCSSFrameConstructor::ContentAppended null-checks its arg aContainer before using it in most cases, e.g.:
> #ifdef MOZ_XUL
>   if (aContainer) {
>     int32_t namespaceID;
>     nsIAtom* tag =
>       mDocument->BindingManager()->ResolveTag(aContainer, &namespaceID);
https://dxr.mozilla.org/mozilla-central/rev/45692c884fdd5136a64fb2f8a61a0c8183b69331/layout/base/nsCSSFrameConstructor.cpp#7484-7488

But there's one recently-added check where it does not null-check:
>   bool isNewlyAddedContentForServo = aContainer->IsStyledByServo() &&
>                                      !aForReconstruction;
https://dxr.mozilla.org/mozilla-central/rev/45692c884fdd5136a64fb2f8a61a0c8183b69331/layout/base/nsCSSFrameConstructor.cpp#7503-7504

We should probably add a null-check there for consistency.

(Or, alternately, we should remove all the old null-checks and add an assertion that the arg must be non-null.  From a quick skim of the callsites, it seems like all of the callers already ensure/assume the arg is non-null.)