RFR: 8276721: G1: Refine G1EvacFailureObjectsSet::iterate [v2]

[Hamlin Li]

> Currently, G1EvacFailureObjectsSet::iterate(ObjectClosure* closure) is not a const method, but it looks like a const method. It will be a surprise for reader, i.e. you would not expect that an iteration method is destructive, clearing out the set it just iterated over.
> We should refine it in some way.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Fix typos

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6303/files
  - new: https://git.openjdk.java.net/jdk/pull/6303/files/d496ded4..4b33882b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6303&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6303&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6303.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6303/head:pull/6303

PR: https://git.openjdk.java.net/jdk/pull/6303