Unify (Pre)Parser::ParseObjectLiteral and add tests.

Notes:
- The regexp in the ParseObjectLiteralComment was wrong, made it less wrong (
it's still wrong since trailing commas are not required / allowed).
- Change in logic: In case we have "get somekeyword() { }", the "somekeyword"
was not logged as a symbol by PreParser and not expected in the preparser data
by Parser. This is unnecessary complication; in other contexts where keywords
are allowed as identifiers, they are logged as symbols (see
ParseIdentifierName).

BUG=v8:3126
LOG=N
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/173273006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19750 ce2b1a6d-e550-0410-aec6-3dcde31c8c00