RFR: JDK-8266802: Shenandoah: Round up region size to page size unconditionally [v2]

[Aleksey Shipilev]

> Since JDK-8265239, runtime/os/TestTracePageSizes.java fails with Shenandoah like this:
> 
> 
> # Internal Error (/home/buildbot/worker/test-jdkX-linux/build/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp:156), pid=55712, tid=55720
> # assert(_num_regions == (max_byte_size / reg_size_bytes)) failed: Must match
> 
> 
> This is because Shenandoah region sizes are rounded up to page size only when `ShenandoahUncommit` is true. In the failing test configuration, `ShenandoahUncommit` is false, because Xmx == Xms.
> 
> Additional testing:
>  - [x] New regression test, now passes
>  - [x] `tier1` with Shenandoah

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8266802-shenandoah-region-size
 - Minor whitespace
 - Fix and regression tests

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3945/files
  - new: https://git.openjdk.java.net/jdk/pull/3945/files/94d4f023..96a4778b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3945&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3945&range=00-01

  Stats: 722 lines in 17 files changed: 390 ins; 203 del; 129 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3945.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3945/head:pull/3945

PR: https://git.openjdk.java.net/jdk/pull/3945