RFR: 8252888: Simplify G1MMUTracker class hierarchy

[Kim Barrett]

> On Sep 18, 2020, at 2:47 PM, Albert Mingkun Yang <ayang at openjdk.java.net> wrote:
> 
> On Wed, 16 Sep 2020 23:19:56 GMT, John Tortugo <github.com+2249648+JohnTortugo at openjdk.org> wrote:
> 
>> 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.
> 
> I think it's better to use `G1MMUTracker` as the type name and mention its queue implementation in the comments,
> instead of including "Queue" in its name.

+1

G1MMUTracker is what it is.  That there is a queue involved is an implementation detail.

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