Please describe the problem:
Magnifier works in half screen magnification, several applications are running.
Press Alt+Tab to invoke app switch dialog, you will find this dialog ride on the
border of source screen and magnified screen, half of this dialog can be
magnified on magnified screen while the left can not be.

Steps to reproduce:
1. Enable desktop accessibility support.
2. Invoke several applications, say web browser, terminal, email client and etc.
3. Press Alt+Tab to switch applications.


Actual results:
The application switch dialog should be put in the middle of source screen, and
can be magnified in magnified screen.

Expected results:
The application switch dialog is riding on the border of source screen and
magnified screen, only half of this dialog can be magnified.

Does this happen every time?
Yes.

Other information:
This bug can be found on vermillion_39/snv_38.