RFR: JDK-8256725: Metaspace: better blocktree and binlist asserts

[Thomas Stuefe]

This is a re-post of https://github.com/openjdk/jdk/pull/1339. It was approved and I integrated, but apparently deleted the branch too soon and interrupted the integration.

May I have approvals again please? Patch is unchanged from the final version of https://github.com/openjdk/jdk/pull/1339.

Thanks!

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Commit messages:
 - JDK-8256725-better-blocktree-asserts-2

Changes: https://git.openjdk.java.net/jdk/pull/1398/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1398&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256725
  Stats: 175 lines in 5 files changed: 131 ins; 15 del; 29 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1398.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1398/head:pull/1398

PR: https://git.openjdk.java.net/jdk/pull/1398