RFR: 8252796: Lanai: Shape clip test artifacts on MacBook Air 2020

[Alexey Ushakov]

Wait for previous ops results before rendering clip spans

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Commit messages:
 - 8252796: Lanai: Shape clip test artifacts on MacBook Air 2020

Changes: https://git.openjdk.java.net/lanai/pull/105/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=105&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252796
  Stats: 4 lines in 2 files changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/lanai/pull/105.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/105/head:pull/105

PR: https://git.openjdk.java.net/lanai/pull/105