RFR: 8273372: More precise ResourceMark in ReferenceProcessor

[Albert Mingkun Yang]

Simple change of moving `ResourceMark` closer to where it is actually required.

Test: tier1-6

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Commit messages:
 - resource-mark

Changes: https://git.openjdk.java.net/jdk/pull/5375/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5375&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273372
  Stats: 15 lines in 3 files changed: 5 ins; 3 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5375.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5375/head:pull/5375

PR: https://git.openjdk.java.net/jdk/pull/5375