Chrome Version: 65.0.3325.181 (Developer Build) Fedora Project (64-bit)
Other browsers tested:
  Add OK or FAIL after other browsers where you have tested this issue:
     Safari: FAIL
    Firefox: OK
    IE/Edge: Unknown

See the test in https://github.com/w3c/web-platform-tests/pull/10429.

https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-setpropertyvalue always
ends up in https://drafts.csswg.org/cssom/#update-style-attribute-for (step 8),
which calls https://dom.spec.whatwg.org/#concept-element-attributes-set-value,
which does queue a mutation record even if the value doesn't change.

This makes this consistent with setAttribute("style", getAttribute("style")),
for example.