This introduces ClassLiteralProperty and a supertype LiteralProperty of
it and ObjectLiteralProperty. It also splits the parsing of the two.
This substiantially clarifies some logic, especially as classes
continue to evolve, and is also about a 2% performance improvement to
parsing either kind of property (since no work is wasted on logic
only necessary for the other kind). Also, it saves a word on
ObjectLiteralProperties.

Review-Url: https://codereview.chromium.org/2302643002
Cr-Commit-Position: refs/heads/master@{#39219}