<Swing Dev> RFR: JDK-8253543: sanity/client/SwingSet/src/ButtonDemoScreenshotTest.java…

[Alexandre Iline]

… failed with "AssertionError: All pixels are not black"

Added a few synchronization points to the test:
	1	wait for the screen to change where the test window is displayes
	2	wait for the image to get still (i.e. painted complete)
	3	wait for the image to change after the mouse move
	4	wait for the image change and then to get still after the mouse press
	5	wait for the image to change after the mouse release

@mrserb Can you take a look?

-------------

Commit messages:
 - JDK-8253543: sanity/client/SwingSet/src/ButtonDemoScreenshotTest.java failed with "AssertionError: All pixels are not black"

Changes: https://git.openjdk.java.net/jdk/pull/389/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=389&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253543
  Stats: 142 lines in 5 files changed: 97 ins; 18 del; 27 mod
  Patch: https://git.openjdk.java.net/jdk/pull/389.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/389/head:pull/389

PR: https://git.openjdk.java.net/jdk/pull/389