RFR: 8259778: Merge MutableSpace and ImmutableSpace [v3]

[Kim Barrett]

> Please review this change which merges ImmutableSpace into MutableSpace,
> eliminating the former.  There were no interesting uses of ImmutableSpace,
> other than as the base class for MutableSpace.  The name ImmutableSpace is
> kind of a misnomer given that usage.
> 
> Testing:
> mach5 tier1-3

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 merge_spaces
 - fix comment
 - remove immutablespace

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2271/files
  - new: https://git.openjdk.java.net/jdk/pull/2271/files/c957962b..56d5d989

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2271&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2271&range=01-02

  Stats: 14767 lines in 242 files changed: 2780 ins; 3810 del; 8177 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2271.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2271/head:pull/2271

PR: https://git.openjdk.java.net/jdk/pull/2271