RFR: 8291718: Remove mark_for_deoptimization from klass unloading [v4]

[Axel Boldt-Christmas]

> @stefank suggested creating a separate issue for this part of [JDK-8291237](https://bugs.openjdk.org/browse/JDK-8291237) 
> 
> Description from the original issue: 
>> The klass unloading code currently sets the mark for deoptimzation flag on nmethods that depend on the klass being unloaded. That however is all it does, there is no guarantee that those nmethods will become not entrant and make_deoptimized. The current implementation may if some future deoptimization happens to trigger see these marks as it scans the whole code cache, but it is never triggered from klass unloading. 
>> 
>> Me and [~eosterlund] discussed this and this behaviour seems like some leftover from earlier versions of klass unloading. There should be no reason to eliminate the nmethods that depend on unloaded klasses except to eliminate dead code. It is probably better to let other mechanisms decide if an nmethod with dead code should be deoptimized than the klass unloading. 
>> 
>> It might be a future improvement to have some stats which record that an nmethod had some dependency to an unloaded klass which might effect the heuristic for selecting what methods are deoptimized.
> 
> Testing: Tier 1-3, 4-7 non-windows
> Windows tier 4-7 still queued

Axel Boldt-Christmas has updated the pull request incrementally with two additional commits since the last revision:

 - Fix indentation
 - Revert "Simplify and assert in remove_all_dependents"
   
   This reverts commit 0141b28d3b30745da31e12a4489ac71e14bd18e2.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9713/files
  - new: https://git.openjdk.org/jdk/pull/9713/files/d94258d0..048f2f71

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9713&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9713&range=02-03

  Stats: 8 lines in 1 file changed: 7 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9713.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9713/head:pull/9713

PR: https://git.openjdk.org/jdk/pull/9713