[css-typed-om] Don't crash for unrepresentable shorthands
ComputedStylePropertyMap::SerializationForShorthand for some reason
expects that CSSValueFromComputedStyle can't return nullptr, when in
reality this can easily happen as soon as you have a shorthand
which can't represent the currently held longhands.
We have likely exercised this code for a long time, but ever since
CL:5577948, we began crashing, since NOTREACHED() is fatal now.
Looking briefly over the spec, it is not defined what to return in
this situation, hence adding a crash test which doesn't make assertions
about the return value.
Fixed: 364443014
Change-Id: I5c6bcc4ef75285194aed2fc0a6b57429655c7610
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5840236
Reviewed-by: Rune Lillesveen futhark@chromium.org
Commit-Queue: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1352461}