RFR: 7903328: Introduce a new method 'clear' in interface 'Multiset' [v2]

[Guoxiong Li]

> Hi all,
> 
> This patch adds a method named `clear` in interface `Multset` and implements the method in its sub-class. A corresponding test case is added and all the test passed locally.
> 
> Thanks for taking the time to review.
> 
> Best Regards,
> -- Guoxiong

Guoxiong Li has updated the pull request incrementally with one additional commit since the last revision:

  Remove null check.

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

Changes:
  - all: https://git.openjdk.org/jmh/pull/81/files
  - new: https://git.openjdk.org/jmh/pull/81/files/a740725e..7c765af2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmh&pr=81&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmh&pr=81&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jmh/pull/81.diff
  Fetch: git fetch https://git.openjdk.org/jmh pull/81/head:pull/81

PR: https://git.openjdk.org/jmh/pull/81