Move all the AtomicString hash logic into AtomicStringTable.

This makes the code more clear by separating it from AtomicString itself. It will
also allow us to do some clever things like storing a reference to the table in
the PerIsolateData and skipping the TLS lookups in the bindings.

Review-Url: https://codereview.chromium.org/2110813003
Cr-Commit-Position: refs/heads/master@{#403066}
9 files changed