Handle the "synchronous case" by marking try/catch blocks introduced for
async functions as ASYNC_AWAIT and traversing up the stack, finding successive
Promises and returning caught if any of them are predicted to be caught.

BUG=v8:5167

Review-Url: https://codereview.chromium.org/2325813002
Cr-Commit-Position: refs/heads/master@{#39433}