Review request for 8047288: [macosx] Endless loop in EDT on Mac

[artem malinko]

Hello, AWT Team.

Please review a fix for the issue:
https://bugs.openjdk.java.net/browse/JDK-8047288
The fix is available at:
http://cr.openjdk.java.net/~mcherkas/artem/8047288/webrev.01/ 
<http://cr.openjdk.java.net/%7Emcherkas/artem/8047288/webrev.01/>

Window.isFocusableWindow() could lead to deadlock if it is invoked on 
AppKit thread. Fix caches result of Window.isFocusableWindow() on a peer 
level and method is not invoked on AppkitThread.

Thank you.