RFR: 8237567: Refactor G1-specific code in shared VM_CollectForMetadataAllocation [v2]

[Ivan Walulya]

> Hi all,
> 
> Please review this refactoring change to move G1 specific code out of VM_CollectForMetadataAllocation. 
> 
> Testing: Tier 1-3.

Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:

  Thomas review

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5282/files
  - new: https://git.openjdk.java.net/jdk/pull/5282/files/b8827b66..13c7bf74

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5282&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5282&range=00-01

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5282.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5282/head:pull/5282

PR: https://git.openjdk.java.net/jdk/pull/5282