Populates sourceDevice attribute into MouseEvent

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

Index: LayoutTests/fast/events/uievent-with-inputdevice.html
diff --git a/LayoutTests/fast/events/uievent-with-inputdevice.html b/LayoutTests/fast/events/uievent-with-inputdevice.html
index d5ef4d67d12af2d22e49541a49af41a1b2e8085f..0f7ac7e6eabc785562f1cbfe7608c15c9e562a76 100644
--- a/LayoutTests/fast/events/uievent-with-inputdevice.html
+++ b/LayoutTests/fast/events/uievent-with-inputdevice.html
@@ -2,6 +2,7 @@
 <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");  
@@ -14,8 +15,26 @@
     shouldBeNonNull("uievent.sourceDevice");
     shouldBeTrue("uievent.sourceDevice.firesTouchEvents");
     
+    // Creating TouchEvent.
     var touchevent = document.createEvent("TouchEvent");
     shouldBeNonNull("touchevent");
     shouldBeNull("touchevent.sourceDevice");
+    
+    // Creating MouseEvent.
+    document.addEventListener("mousedown", function(event) {
+      shouldBeNonNull("event");
+      shouldBeNull("event.sourceDevice");
+    });
+
+    var e = new MouseEvent('mousedown');
+    document.dispatchEvent(e);
+    
+    var sourceDevice = new InputDevice({ firesTouchEvents: false });
+    shouldBeFalse("sourceDevice.firesTouchEvents");
+    
+    var mouseevent = document.createEvent("MouseEvents");
+    mouseevent.initMouseEvent("mousedown", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null, sourceDevice);

[Rick Byers, 2015/06/23 00:55:57]

nit: please use the 'new MouseEvent' style instead or as well (just like the
'new UIEvent' above).  If we're only going to test one of the patterns than the
modern style is probably the one we really care about.

[lanwei, 2015/06/23 22:19:20]

Done.

+    shouldBeNonNull("mouseevent.sourceDevice");
+    shouldBeFalse("mouseevent.sourceDevice.firesTouchEvents");
 
-</script>
+</script>