Put try/catch around the dangerous part of CallSiteToString.
If it fails, at least we have the file/line/column information.

(This addresses V8:2757, https://code.google.com/p/v8/issues/detail?id=2757.)
Backport this bugfix from v8 that came in around version v3.19.13 (and
showed up in node v0.11.3).

https://codereview.chromium.org/16286018/

This gets rid of long GC pauses caused by processing weakmaps too many
times during a garbage collection.