RFR: 8274939: Incorrect size of the pixel storage is used by the robot on macOS

[Sergey Bylokhov]

In JDK 9 the native code for the robot class was reworked to get an access to the HiDPI quality screenshots. So we allocate the data storage for the HiDPI quality and then request the best quality from the macOS.

It works fine if the user request the screenshot of some area, since we properly scale this area. Unfortunately it does not work well if the user request only one pixel, in this case we allocate the array of one element and does not multiply the size by the scale, so if the system scale is 2 then the macOS returns the 2x2 pixels, which does not fit properly to the array of one element. This can be checked by the Xcheck:jni option which produce fatal error in this case.

Solution is to allocate the storage of the proper size 1 * scale * 1 * scale

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Commit messages:
 - Initial fix JDK-8274939

Changes: https://git.openjdk.java.net/jdk/pull/5864/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5864&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274939
  Stats: 6 lines in 2 files changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5864.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5864/head:pull/5864

PR: https://git.openjdk.java.net/jdk/pull/5864