RFR: 8252888: Collapse G1MMUTracker class hierarchy [v3]

[John Tortugo]

> Relates to: https://bugs.openjdk.java.net/browse/JDK-8252888
> Tested on: x86_64 - Linux - tier1
> Need sponsor: yes
> 
> Merge `G1MMUTracker` and `G1MMUTrackerQueue` into a single class and make method members non virtual.

John Tortugo has updated the pull request incrementally with one additional commit since the last revision:

  Address PR feedback. Formatting issues.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/214/files
  - new: https://git.openjdk.java.net/jdk/pull/214/files/136a1ae7..bd194ef6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=214&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=214&range=01-02

  Stats: 18 lines in 1 file changed: 4 ins; 2 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/214.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/214/head:pull/214

PR: https://git.openjdk.java.net/jdk/pull/214