RFR: 6810: Create treemap viewer for JOverflow [v6]

[Kangcheng Xu]

On Mon, 22 Jun 2020 19:03:37 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> What is the intended distribution model? Should this be something from the update site, or delivered as part of the
>> standard offering?
>
> If part of standard JOverflow, then you might as well put it in the JOverflow bundle. It can still be optional to open
> the view. If you want this to be an optional bundle from the update sites, then you need to add them to the update
> sites. Personally I think this might as well be part of JOverflow directly.

@thegreystone I think it makes more sense to be part of JOverflow directly. I've made changes to relocate treemap files
and to remove the ext.treemap module.

Please give it a quick look. Thanks!

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PR: https://git.openjdk.java.net/jmc/pull/77