Handle some examples of the "asynchronous case" by marking await expressions
as either caught or uncaught; in the caught case, this marks the Promise passed
in as having a catch predicted. The marking is done in AST numbering, which
chooses between two different runtime function calls based on catch prediction.

BUG=v8:5167

Review-Url: https://codereview.chromium.org/2276243002
Cr-Commit-Position: refs/heads/master@{#39394}