fn3 review

- adds dartdocs
- replaces config setter with didUpdateConfig() so that you can't replace
the config outside of the system
- renames didUnmount() with destroy().
- rename Component to StatelessComponent, ComponentConfiguration to
StatefulComponent
- move debug dump to end of file
- renamed _holder to _element

packages/unit/test/fn3/stateful_component_test.dart

@@ -4,7 +4,7 @@ import 'package:test/test.dart';
 
 import 'widget_tester.dart';
 
-class TestComponentConfig extends ComponentConfiguration {
+class TestComponentConfig extends StatefulComponent {
   TestComponentConfig({ this.left, this.right });
 
   final Widget left;
@@ -13,9 +13,7 @@ class TestComponentConfig extends ComponentConfiguration {
   TestComponentState createState() => new TestComponentState();
 }
 
-class TestComponentState extends ComponentState {
-  TestComponentConfig get config => super.config;
-
+class TestComponentState extends ComponentState<TestComponentConfig> {
   bool _showLeft = true;
 
   void flip() {
@@ -32,7 +30,7 @@ class TestComponentState extends ComponentState {
 final BoxDecoration kBoxDecorationA = new BoxDecoration();
 final BoxDecoration kBoxDecorationB = new BoxDecoration();
 
-class TestBuildCounter extends Component {
+class TestBuildCounter extends StatelessComponent {
   static int buildCount = 0;
 
   Widget build() {
@@ -42,8 +40,8 @@ class TestBuildCounter extends Component {
 }
 
 void flipStatefulComponent(WidgetTester tester) {
-  ComponentStateElement stateElement =
-      tester.findElement((element) => element is ComponentStateElement);
+  StatefulComponentElement stateElement =
+      tester.findElement((element) => element is StatefulComponentElement);
   (stateElement.state as TestComponentState).flip();
 }
 

packages/unit/test/fn3/widget_tester.dart

 import 'package:sky/src/fn3/framework.dart';
 
-class TestComponent extends Component {
+class TestComponent extends StatelessComponent {
   TestComponent({ this.child });
   final Widget child;
   Widget build() => child;
@@ -9,7 +9,7 @@ class TestComponent extends Component {
 final Object _rootSlot = new Object();
 
 class WidgetTester {
-  ComponentElement _rootElement;
+  StatelessComponentElement _rootElement;
 
   void walkElements(ElementVisitor visitor) {
     void walk(Element element) {
@@ -36,7 +36,7 @@ class WidgetTester {
 
   void pumpFrame(Widget widget) {
     if (_rootElement == null) {
-      _rootElement = new ComponentElement(new TestComponent(child: widget));
+      _rootElement = new StatelessComponentElement(new TestComponent(child: widget));
       _rootElement.mount(_rootSlot);
     } else {
       _rootElement.update(new TestComponent(child: widget));