RFR: 8295012: Arena should not derive from CHeapObj<mtNone> [v3]

[Kim Barrett]

> Please review this change to the `Arena` class.  Rather than deriving from
> `CHeapObj<mtNone>` (which has the effect of preventing C-heap allocation for an
> arena by asserting if such is attempted), instead have no allocation base
> class so that `new Arena(...)` will fail to compile.
> 
> Testing: mach5 tier1

Kim Barrett 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 arena-base
 - Arena derives from CHeapObjBase
 - remove base class from Arena

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10621/files
  - new: https://git.openjdk.org/jdk/pull/10621/files/828541f5..817072dd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10621&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10621&range=01-02

  Stats: 5303 lines in 121 files changed: 3625 ins; 818 del; 860 mod
  Patch: https://git.openjdk.org/jdk/pull/10621.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10621/head:pull/10621

PR: https://git.openjdk.org/jdk/pull/10621