style: Use cbindgen for content property.

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

components/style/gecko_string_cache/namespace.rs

@@ -25,6 +25,7 @@ macro_rules! ns {
 
 /// A Gecko namespace is just a wrapped atom.
 #[derive(Clone, Debug, Default, Eq, Hash, MallocSizeOf, PartialEq, ToShmem)]
+#[repr(transparent)]
 pub struct Namespace(pub Atom);
 
 impl PrecomputedHash for Namespace {