Web Inspector: HeapSnapshot: introduce performance counter for HeapSnapshotConstructo...

Web Inspector: HeapSnapshot: introduce performance counter for HeapSnapshotConstructorsDataGrid._aggregatesReceived method.
https://bugs.webkit.org/show_bug.cgi?id=87393

Reviewed by Yury Semikhatsky.

PerformanceTests:

* inspector/heap-snapshot.html:

Source/WebCore:

* inspector/front-end/HeapSnapshotDataGrids.js:
(WebInspector.HeapSnapshotConstructorsDataGrid.prototype._aggregatesReceived):
(WebInspector.HeapSnapshotConstructorsDataGrid.prototype._populateChildren):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@118523 268f45cc-cd09-0410-ab3c-d52691b4dbfc