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.")
 
     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");
+    
+    var keyboardevent = document.createEvent("KeyboardEvent");
+    shouldBeNonNull("keyboardevent");
+    shouldBeNull("keyboardevent.sourceDevice");
+    
+    var sourceDevice = new InputDevice({ firesTouchEvents: false });
+    shouldBeFalse("sourceDevice.firesTouchEvents");
+    
+    keyboardevent.initKeyboardEvent("keydown", true, true, null, 0, 0, false, false, false, false, sourceDevice);
+    shouldBeNonNull("keyboardevent.sourceDevice");
+    shouldBeFalse("keyboardevent.sourceDevice.firesTouchEvents");
 
-</script>
+</script>