RFR: 8297195: AWTAccessor and SwingAccessor should avoid double racy reads from non-volatile fields

[Sergey Bylokhov]

The patch applied to SharedSecrets by https://github.com/openjdk/jdk/pull/1914 is applied to the AWTAccessor and SwingAccessor. It prevents null to be returned by the some of methods. 

See also discussion in thread: https://mail.openjdk.java.net/pipermail/core-libs-dev/2020-December/072798.html

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Commit messages:
 - Update AWTAccessor.java
 - 8297195: AWTAccessor and SwingAccessor should avoid double racy reads from non-volatile fields

Changes: https://git.openjdk.org/jdk/pull/11205/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11205&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297195
  Stats: 156 lines in 2 files changed: 74 ins; 6 del; 76 mod
  Patch: https://git.openjdk.org/jdk/pull/11205.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11205/head:pull/11205

PR: https://git.openjdk.org/jdk/pull/11205