RFR: JDK-8202790: DnD test DisposeFrameOnDragTest.java does not clean up [v2]

[Alisen Chung]

> Added a background to the test to prevent the file from dragging onto the desktop and creating an extra file.

Alisen Chung has updated the pull request incrementally with one additional commit since the last revision:

  changed button mask to button down mask

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8370/files
  - new: https://git.openjdk.java.net/jdk/pull/8370/files/e9dace84..795d2a2d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8370&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8370&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8370.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8370/head:pull/8370

PR: https://git.openjdk.java.net/jdk/pull/8370