Some events are not handled while the print window is active

[maxnikulin]

In chromium (linux) some page elements become inactive
while the print window is open.

It may be reproduced using tests/test_grid_printer.html
Click Print button and ensure that the popup is not blocked.
Switch back to original browser window.
At the first glance it looks OK, grid controls
mostly work properly. Try to check "Use CSS String".
Text area does not appear if print window is open.
Close the print popup and check again.

Print popup should be somehow fully detached
from the original tab or grid appearance should
be changed to clearly indicate that print is active
to avoid user confusion by partially functional controls.