test(*): run class-related tests everywhere; fix eval syntax

1. Wrap an evaled class definition in parens; previously they weren't; the test
   wasn't failing only because it was disabled everywhere outside of Chrome
   and Chrome <59 incorrectly accepted such input.
2. There's no reason to restrict class-related tests just to Chrome; now they
   run in every browser that supports ES6 classes. The classes support test
   was modified to check not only if a class definition parses but also if
   it stringifies correctly which is required by AngularJS. This restriction
   disables class-related tests in current Firefox (53) but will work in v55
   or newer.

Closes #15967