Investigate possibility of lazily computing CSS about alfa HOT 2 CLOSED

I recently backtracked a bit on this issue in 280a3b6 which changed the way style declarations are parsed. Now, parsing of supported properties is done eagerly in order to more easily support shorthand properties. Previously, when asked for a property foo, we would look for all declarations of property foo and pick the last valid declaration. With the introduction of support for sorthand properties, this became a little more tricky as the property foo could also result from a shorthand declaration such as bar. When looking for the property foo, we would therefore also have to look for the property bar and check if any such declarations result in a foo. Additionally, a declaration such as bar might also result in other properties being declared, such as baz, which we would then also have to deal with to avoid having to parse bar declarations for both foo and baz lookups.

from alfa.

I did some more investigation into this as part of #447 and have concluded that further attempts to delay parts of style resolution likely won't pay off. We need to perform at least a baseline cascade eagerly to benefit from ancestor filtering and need to also eagerly parse properties per my previous comment. The current architecture doesn't seem to support any further laziness.

from alfa.