We have been working on implementing constructors of Events. ErrorEvent has a constructor in JSC (https://bugs.webkit.org/show_bug.cgi?id=67924), but do not have it in V8.
Created attachment 107812 [details] Patch
I confirmed that fast/events/constructors/error-event-constructor.html passes clang build. The numerical conversion problem (https://bugs.webkit.org/show_bug.cgi?id=67980) seems to happen on an unsigned long long value but not to happen on an unsigned long value.
Created attachment 108984 [details] rebased patch for commit
Comment on attachment 108984 [details] rebased patch for commit Clearing flags on attachment: 108984 Committed r96208: <http://trac.webkit.org/changeset/96208>