RFR: 8272093: Extract evacuation failure injection from G1CollectedHeap

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that extracts out the evacuation failure injection mechanism from `G1CollectedHeap` into its own class?
This reduces the amount of code in `G1CollectedHeap` a bit, moving somewhat uninteresting but somewhat important (testing) code out from there. Also documented it a bit. The other reason was that imho it stuck out a bit due to the ifdef's in `G1CollectedHeap`.

I checked that gcc does compile out the call to `evacuation_should_fail()` in `G1ParScanThreadState` in product mode.

Testing: tier1, local testing

Thanks,
  Thomas

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Commit messages:
 - Fix initialization order issue with injector
 - Extract evac failure injector from G1CollectedHeap

Changes: https://git.openjdk.java.net/jdk/pull/5047/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5047&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272093
  Stats: 329 lines in 7 files changed: 212 ins; 114 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5047.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5047/head:pull/5047

PR: https://git.openjdk.java.net/jdk/pull/5047