This issue was originally filed by @chalin

What steps will reproduce the problem?

1. Consider the following code

    // Context: import 'dart:html' as dom;
    var element = dom.querySelector(...);
    var ev = new KeyEvent('keypress', keyCode: 65);
    
2. print("ev=$ev, and (ev is Event) is ${ev is Event}");
    ==> output: ev=Instance of 'KeyEvent', and (ev is Event) is true
   
3. element.dispatchEvent(ev);
    ==> yields
    Caught Invalid class: expected instance of Event
    #­0 Node.dispatchEvent (.../dart/dart/html/Node.dart:586)

What is the expected output? What do you see instead?

The exception reports that ev is not an instance of Event and yet from the printed output we see that it is.

What version of the product are you using? On what operating system?

Dartium Version 33.0.1750.48 (251129)
Dart VM version: 1.2.0-dev.4.0 (Fri Feb 7 10:19:23 2014) on "macos_x64"

Please provide any additional information below.

The problem might be that KeyEvents cannot be dispatched for some other reason, and if so, then the thrown exception message should be changed.