Bug 201906 [Viewers] 3.4 ColumnViewerEditor leaks ViewerCell instances.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewerEditor.java
} else if ((feature & TABBING_HORIZONTAL) == TABBING_HORIZONTAL) {
				cell2edit = searchNextCell(row, row.getCell(columnIndex), row
						.getCell(columnIndex), viewer);
			}
		}
		if (cell2edit != null) {
			viewer.getControl().setRedraw(false);
			ColumnViewerEditorActivationEvent acEvent = new ColumnViewerEditorActivationEvent(
					cell2edit, event);
			viewer.triggerEditorActivationEvent(acEvent);
			viewer.getControl().setRedraw(true);
		}
	}
	private ViewerCell searchCellAboveBelow(ViewerRow row, ColumnViewer viewer,
			int columnIndex, boolean above) {
		ViewerCell rv = null;
		ViewerRow newRow = null;
		if (above) {
			newRow = row.getNeighbor(ViewerRow.ABOVE, false);
		} else {
			newRow = row.getNeighbor(ViewerRow.BELOW, false);
		}
		if (newRow != null) {
			ViewerColumn column = viewer.getViewerColumn(columnIndex);
			if (column != null
					&& column.getEditingSupport() != null
					&& column.getEditingSupport().canEdit(
							newRow.getItem().getData())) {
				rv = newRow.getCell(columnIndex);
			} else {