RFR: 8259778: Merge MutableSpace and ImmutableSpace [v2]

[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 incrementally with one additional commit since the last revision:

  fix comment

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2271/files
  - new: https://git.openjdk.java.net/jdk/pull/2271/files/e1d95459..c957962b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2271&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2271&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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