Background: We are planning to make all Events constructable. For example, CustomEvent already has the spec for its constructor (http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-customevent).

We propose a spec for ErrorEvent constructor as follows:

[Constructor(DOMString type, optional ErrorEventInit eventInitDict)]
dictionary ErrorEventInit : EventInit {
    DOMString message;
    DOMString filename;
    unsigned long lineno;
}