Implement `MallocSizeOf` for cssparser types (#399) #349

Job	Run time
Linux (nightly)	2m 33s
Linux (nightly, --features dummy_match_byte)	2m 33s
Linux (nightly, --features malloc_size_of)	2m 32s
Linux (beta)	30s
Linux (beta, --features dummy_match_byte)	31s
Linux (beta, --features malloc_size_of)	32s
Linux (stable)	32s
Linux (stable, --features dummy_match_byte)	32s
Linux (stable, --features malloc_size_of)	35s
Linux (1.63.0)	2m 51s
Linux (1.63.0, --features dummy_match_byte)	2m 48s
Linux (1.63.0, --features malloc_size_of)	2m 50s
Linux (nightly, --features bench)	5m 54s
Linux (nightly, --features bench,dummy_match_byte)	6m 2s
Result	1s
	31m 16s

Provide feedback