Draggable Tests: fix IE offset tests affected by focus issues.

Calling element.focus() causes scroll in IE. In order to correctly test scroll behavior,
we must rely on the actual calculated offset instead of the helper offset to ensure
cross browser test consistency.

Author: mikesherov

tests/unit/draggable/draggable_test_helpers.js

@@ -46,7 +46,7 @@ TestHelpers.draggable = {
 	shouldMovePositionButNotOffset: function( el, msg, handle ) {
 		handle = handle || el;
 		TestHelpers.draggable.testDragPosition( el, 100, 100, 100, 100, msg );
-		TestHelpers.draggable.testDragOffset( el, 100, 100, 0, 0, msg );
+		TestHelpers.draggable.testDragHelperOffset( el, 100, 100, 0, 0, msg );
 
 		$( handle ).simulate( "drag", {
 			dx: 100,