[9] Review Request: 7148531 [macosx] In test, the window does not have time to resize before make a screenshot

[Sergey Bylokhov]

Hello.
Please review the fix for jdk 9.
- Frame was changed to undecorated to solve a rounded corners(which was 
a main issue) + moved to the center of the screen.
- waitForIdle() was added.
- Typo in incorrect color validation was fixed.
Bug: https://bugs.openjdk.java.net/browse/JDK-7148531
Webrev can be found at: http://cr.openjdk.java.net/~serb/7148531/webrev.00

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Best regards, Sergey.