Bug 201906 [Viewers] 3.4 ColumnViewerEditor leaks ViewerCell instances.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewerEditor.java
rv = previousCell;
			} else {
				rv = searchPreviousCell(row, previousCell, originalCell, viewer);
			}
		} else {
			if ((feature & TABBING_CYCLE_IN_ROW) == TABBING_CYCLE_IN_ROW) {
				rv = searchPreviousCell(row, null, originalCell, viewer);
			} else if ((feature & TABBING_MOVE_TO_ROW_NEIGHBOR) == TABBING_MOVE_TO_ROW_NEIGHBOR) {
				ViewerRow rowAbove = row.getNeighbor(ViewerRow.ABOVE, false);
				if (rowAbove != null) {
					rv = searchPreviousCell(rowAbove, null, originalCell,
							viewer);
				}
			}
		}
		return rv;
	}
	private ViewerCell searchNextCell(ViewerRow row, ViewerCell currentCell,
			ViewerCell originalCell, ColumnViewer viewer) {
		ViewerCell rv = null;
		ViewerCell nextCell;
		if (currentCell != null) {
			nextCell = currentCell.getNeighbor(ViewerCell.RIGHT, true);
		} else {
			nextCell = row.getCell(row.getCreationIndex(0));
		}
		
		if (originalCell.equals(nextCell)) {
			return null;
		}