MutationRecord should be exposed on window but not constructable

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

PASS window.MutationRecord is non-null.
PASS typeof MutationRecord is "function"
PASS new MutationRecord threw exception TypeError: Illegal constructor.
PASS record instanceof MutationRecord is true
PASS successfullyParsed is true

TEST COMPLETE