RFR: JDK-8298084: Memory leak in Method::build_profiling_method_data [v6]

[Justin King]

> Resolve memory leak related to `MethodData::_extra_data_lock` in `Method::build_profiling_method_data` by calling `MethodData::~MethodData()`.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Add comment to metaprogramming usage
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11526/files
  - new: https://git.openjdk.org/jdk/pull/11526/files/1fc897dc..d745f437

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11526&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11526&range=04-05

  Stats: 6 lines in 1 file changed: 2 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11526.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11526/head:pull/11526

PR: https://git.openjdk.org/jdk/pull/11526