RFR: 8273251: Call check_possible_safepoint() from SafepointMechanism::process_if_requested()

[Patricio Chilano Mateo]

Hi,

Please review this small fix to call check_possible_safepoint() from SafepointMechanism::process_if_requested() and remove the same call from transition_and_process(). See the bug description for more detail.
Since there were only two lines left of common code from transition_from_native() and transition_from_vm() I just removed transition_and_process() altogether. This also saves an unneeded extra transition to _thread_in_vm when transitioning from vm to Java.

Testing tiers 1-6.

Thanks,
Patricio

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Commit messages:
 - v1

Changes: https://git.openjdk.java.net/jdk/pull/5342/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5342&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273251
  Stats: 34 lines in 3 files changed: 13 ins; 17 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5342.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5342/head:pull/5342

PR: https://git.openjdk.java.net/jdk/pull/5342