This is in preparation to implementing exception prediction for async
functions.  Each handler table entry can now predict "caught", "uncaught", or
"promise". The latter indicates that the exception will lead to a promise
rejection.

To mark the relevant try-catch blocks, we add a new native syntax.
try { } %catch (e) { } indicates a TryCatchStatement with the "promise"
prediction.

The previous implementation of using the function to tell the relevant
try-catch apart from inner try-catch blocks will not work for async functions
since these can have inner try-catch blocks inside the same function.

BUG=v8:5167

Review-Url: https://codereview.chromium.org/2161263003
Cr-Commit-Position: refs/heads/master@{#37966}