RFR: 8277981: String Deduplication table is never cleaned up due to bad dead_factor_for_cleanup

[Aleksey Shipilev]

See the reproducer and analysis in the bug. 

The root cause for this problem is that `percent_of` returns `0..100` (percent) value of `nominator / denominator`. Which means if we feed `percent` and `100` there, this is an identity operation, returning the same value. And we wanted the conversion from percent to factor instead.

Additional testing:
 - [x] Reproducer stress test does not leak anymore
 - [ ] Linux x86_64 fastdebug tier1

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/6613/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6613&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277981
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6613.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6613/head:pull/6613

PR: https://git.openjdk.java.net/jdk/pull/6613