Dragging, resizing dialogs over frames

[sergeev-av]

Dragging, resizing actions stop after mouse entering "xul:iframe" element.

Steps to reproduce:

1. lanch MainApp
2. start dragging dialog
3. move mouse faster than dialog moving after.

Example:
MainApp: http://pastebin.com/YRHksxrp
Frame: http://pastebin.com/AVZkRAtM