This visibility notification path was unhooked at some point during the refactoring to split into layer/surfaces compositor in the last year or two.  It was rehooked but only for Aura in https://codereview.chromium.org/2238693002, leaving Android with visibility permanently true on the root display compositor.

From a quick memory comparison on Nexus 6P, the memory released by this path on Android is within the noise at moment.  But it's definitely expected to be hooked up to release whatever it's holding.

Foreground nytimes: 
     95,593K: org.chromium.chrome (pid 12479 / activities)
     88,260K: org.chromium.chrome:privileged_process0 (pid 12567)

Background nytimes with fix:
     64,822K: org.chromium.chrome (pid 12932 / activities)
     37,687K: org.chromium.chrome:privileged_process0 (pid 13025)
(again)
     70,994K: org.chromium.chrome (pid 11465 / activities)
     38,451K: org.chromium.chrome:privileged_process0 (pid 11554)

Background nytimes without fix:
     63,843K: org.chromium.chrome (pid 12479 / activities)
     38,577K: org.chromium.chrome:privileged_process0 (pid 12567)