Use private symbols to mark default promise handler, instead of calling out to default
handlers defined in JS. We check for this symbol in PromiseHandle and perform the
appropriate behavior as the default handlers.

Catch prediction logic is updated to account for a symbol.

BUG=v8:5343

Review-Url: https://codereview.chromium.org/2695593002
Cr-Commit-Position: refs/heads/master@{#43135}