Bug 191977

Summary: Table selection should be handled by a SelectionController. This is a step toward adding multiple-selection to TreeOutline in https://webkit.org/b/191483. Notes: The controller and its delegate (a Table or TreeOutline): class SelectionController { constructor(delegate) get allowsMultipleSelection() set allowsMultipleSelection(flag) get lastSelectedItem() get selectedItems() get numberOfItems() hasSelectedItem(index) selectItem(index, extendSelection = false) deselectItem(index) selectAll() deselectAll() removeSelectedItems() clear() didInsertItem(index); didRemoveItem(index); handleKeyDown(event) handleItemMouseDown(index, event) } class SelectionControllerDelegate { // Required selectionControllerNumberOfItems(controller) selectionControllerNextSelectableIndex(controller, index) selectionControllerPreviousSelectableIndex(controller, index) // Optional selectionControllerSelectionDidChange(controller, deselectedItems, selectedItems) }