This cleans up and also allows us to keep the distinction between content: none
and content: normal, which allows us to fix the computed style we return from
getComputedStyle().
Do this last bit from the resolved value instead of StyleAdjuster, because
otherwise we need to tweak every initial struct for ::before / ::after.
Differential Revision: https://phabricator.services.mozilla.com/D58276
This patch replaces the handwritten MallocSizeOf implementation for
PropertyDeclaration with a derived one, which gives much more thorough
measurement.
This requires (a) deriving MallocSizeOf for a *lot* of additional types (most
of which already have `derive(HeapSizeOf)` in Servo builds), and (b)
implementing MallocSizeOf for a few more types in the `malloc_size_of` crate.
These changes would significantly improve the reporting coverage for gmail if
it weren't for the fact that SpecifiedUrl isn't measured due to a lack of
clarity about its fields; that can be fixed as a follow-up once bug 1397971 has
landed.
