This removes the duplicate property check from object literals.
Instead we repurpose the ObjectLiteralChecker into two cases, implemented
by two subclasses to ObjectLiteralCheckerBase called ObjectLiteralChecker
and ClassLiteralChecker.
The object literal checker now only checks for duplicate __proto__ fields in
object literals.
The class literal checker checks for duplicate constructors, non constructor
fields named constructor as well as static properties named prototype.
BUG=v8:3819
LOG=Y
R=adamk, dslomov@chromium.org
Review URL: https://codereview.chromium.org/873823003
Cr-Commit-Position: refs/heads/master@{#26336}
