ENYO-3062:DnD control point disappear in designer

Modified iframe.js

Change
- The point should be visible.

Note
-Step-1) Drag & Drop a button from palette to designer
 Step-2) Drag & Drop the size controller point
 Step-3) Drag & Drop the point to increase maximum to the screen as much as you can

Test Result
 Step 1) controller point does position change.
 Step 2) this is support size from the palette.
 Step 3) The point should be visible.

Enyo-DCO-1.1-Signed-off-by: hgpark uionion@gmail.com