If an exception is thrown when there is a Promise being created, the Promise
catch prediction code would call into a part implemented in JavaScript to see if
the Promise has a catch handler. If it is not possible to call back into JS,
e.g., due to a stack overflow, then this would lead to a crash. This patch
"speculates" that, if it's impossible to call back into JavaScript, then the
error is unhandled, avoding the issue. In a future patch, the catch prediction
logic should be entirely written in C++, but this patch adds a minimal fix to
be more friendly to backports.

BUG=chromium:662935
R=jgruber

Review-Url: https://codereview.chromium.org/2487833002
Cr-Commit-Position: refs/heads/master@{#40851}