Populates sourceDevice attribute into MouseEvent

LayoutTests/fast/events/uievent-with-inputdevice.html

 <script src="../../resources/js-test.js"></script>
 <script>
     description("This tests that UIEvent and its subclass will have sourceDevice set to be null by default, and it can also be passed when initialization.")
 
     var uievent = document.createEvent('UIEvent');
     shouldBeNonNull("uievent");
     shouldBeNull("uievent.sourceDevice");  
     
     uievent = new UIEvent('eventType', { sourceDevice: new InputDevice({ firesTouchEvents: false }) });
     shouldBeNonNull("uievent.sourceDevice");
     shouldBeFalse("uievent.sourceDevice.firesTouchEvents");
     
     uievent = new UIEvent('eventType', { sourceDevice: new InputDevice({ firesTouchEvents: true }) });
     shouldBeNonNull("uievent.sourceDevice");
     shouldBeTrue("uievent.sourceDevice.firesTouchEvents");
     
     var touchevent = document.createEvent("TouchEvent");
     shouldBeNonNull("touchevent");
     shouldBeNull("touchevent.sourceDevice");
+    
+    document.addEventListener("click", function(event) {

[tdresser, 2015/06/12 13:06:54]

The other tests look at mousedown/mousemove/mouseup.
It would probably make sense to test those here as well.

[lanwei, 2015/06/16 21:51:43]

Done.

+      shouldBeNonNull("event");
+      shouldBeNull("event.sourceDevice");
+    });
 
-</script>
+    var e = new MouseEvent('click');
+    document.dispatchEvent(e);
+
+</script>