RFR: JDK-8281000 ClassLoader::registerAsParallelCapable throws NPE if caller is null [v3]

[Tim Prinzing]

> JDK-8281000 ClassLoader::registerAsParallelCapable throws NPE if caller is null

Tim Prinzing has updated the pull request incrementally with one additional commit since the last revision:

  More changes from feedback.
  
  The javadoc is improved to reflect InvalidCallerException is thrown with
  a caller that can't be assigned to a ClassLoader as well as a null
  caller frame.  Added a test IsParallelCapableBadCaller that uses
  reflection hackery to create a case where called with an invalid caller
  on the call stack.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7448/files
  - new: https://git.openjdk.java.net/jdk/pull/7448/files/fa66af15..d67bbb16

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7448&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7448&range=01-02

  Stats: 85 lines in 3 files changed: 74 ins; 5 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7448.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7448/head:pull/7448

PR: https://git.openjdk.java.net/jdk/pull/7448