Currently WebCore::reportException can evaluate JavaScript when handling exceptions. The JS evaluation can itself throw an exception if running code in the page.

For example:

    function MyError() {
        this.name = "MyErrorName";
        this.message = "MyErrorMessage";
    }
    MyError.prototype.toString = function() {
        throw "oops";
    }

    function produceError() {
        throw new MyError();
    }

    produceError();

WebCore::reportException call's this toString, and can potentially get values with hooks in valueOf as well. We should avoid running JS that can trigger its own exceptions if possible.