Populates sourceDevice attribute into KeyboardEvent

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.")
 
     // Creating UIEvent.
     var uievent = document.createEvent('UIEvent');
     shouldBeNonNull("uievent");
     shouldBeNull("uievent.sourceDevice");  
     
     uievent = new UIEvent('eventType', { sourceDevice: new InputDevice({ firesTouchEvents: false }) });
@@ skipping 11 matching lines @@
     
     // Creating MouseEvent.
     var mouseevent = new MouseEvent('mousedown');
     shouldBeNonNull("mouseevent");
     shouldBeNull("mouseevent.sourceDevice");
     
     var mouseevent = new MouseEvent('mousedown', { sourceDevice: new InputDevice({ firesTouchEvents: false }) });
     shouldBeNonNull("mouseevent.sourceDevice");
     shouldBeFalse("mouseevent.sourceDevice.firesTouchEvents");
 
+    
+    // Creating KeyboardEvent.
+    var keyboardevent = new KeyboardEvent("keydown");
+    shouldBeNonNull("keyboardevent");
+    shouldBeNull("keyboardevent.sourceDevice");
+    
+    keyboardevent = new KeyboardEvent("keydown", { sourceDevice: new InputDevice({ firesTouchEvents: false }) });
+    shouldBeNonNull("keyboardevent.sourceDevice");
+    shouldBeFalse("keyboardevent.sourceDevice.firesTouchEvents");
+
 </script>