RFR: 8286396: Address possibly lossy conversions in jdk.management.jfr

[Erik Gahlin]

Could I have a review of two lossy conversion issues.

The size of an event can't be larger than 2^28, so it shouldn't be an issue in practise, but the type id could potentially be larger than 2^31, but it would require a user to load more than 2 billion classes. 

Testing: jdk/jdk/jfr

Thanks
Erik

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

Commit messages:
 - Initial

Changes: https://git.openjdk.java.net/jdk/pull/8603/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8603&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286396
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8603.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8603/head:pull/8603

PR: https://git.openjdk.java.net/jdk/pull/8603