Verify that shadow roots with identical styles share style resolvers (have equal identifier below).
(document resolver (identifier=0) (author rule count=0))
(shadow root resolver (user agent) (identifier=1) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (user agent) (identifier=1) (author rule count=0))

After style mutation
(document resolver (identifier=0) (author rule count=0))
(shadow root resolver (user agent) (identifier=1) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (author) (identifier=4) (author rule count=2))
(shadow root resolver (author) (identifier=5) (author rule count=2))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=2) (author rule count=0))
(shadow root resolver (author) (identifier=3) (author rule count=1))
(shadow root resolver (user agent) (identifier=1) (author rule count=0))