This came up in Polymer 2 testing. Apparently change.review (which has
boolean type) can be undefined, while in Polymer 1 it was always set.
The rationale is that the default should be "reviewed = true", because
something being unreviewed and thus becoming bold is the non-standard
case.
Change-Id: Ie027d9c8830e0d83b8d104261512269c241f2250
65513b0171