RFR: 6810: Create treemap viewer for JOverflow [v3]

[Kangcheng Xu]

On Thu, 11 Jun 2020 20:34:03 GMT, Alex Macdonald <aptmac at openjdk.org> wrote:

>> Kangcheng Xu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fixed failing to create the part's controls due to NPE
>
> application/org.openjdk.jmc.joverflow.ext.treemap/src/main/java/org/openjdk/jmc/joverflow/ext/treemap/TreemapAction.java
> line 69:
>> 68: 		ZOOM_OUT(Messages.TreemapAction_ZOOM_OUT_DESCRIPTION, IAction.AS_PUSH_BUTTON, CoreImages.ZOOM_OUT), //
>> 69: 		ZOOM_OFF(Messages.TreemapAction_ZOOM_OFF_DESCRIPTION, IAction.AS_PUSH_BUTTON, CoreImages.ZOOM_OFF);
>> 70:
> 
> For the zoom off action, I feel like the icon should closer represent something to a "reset" icon, maybe like the one
> JOverflow uses? Otherwise it's not immediately obvious what the button does without reading it's tooltip.

Icon replaced with the one JOverflow uses.

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