RFR: 8275607 G1: G1CardSetAllocator::drop_all needs to call G1SegmentedArray::drop_all

[Hamlin Li]

This is a follow-up of JDK-8273626.

G1CardSetAllocator::drop_all should call call G1SegmentedArray::drop_all to put all buffers into buffer free list, which is the original behavior of G1CardSetAllocator.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/6035/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6035&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275607
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6035.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6035/head:pull/6035

PR: https://git.openjdk.java.net/jdk/pull/6035