Port most of scrollable.dart to fn3

packages/flutter/lib/src/fn3/homogeneous_viewport.dart

@@ -8,7 +8,7 @@ import 'package:sky/rendering.dart';
 import 'package:sky/src/fn3/framework.dart';
 import 'package:sky/src/fn3/basic.dart';
 
-typedef List<Widget> ListBuilder(int startIndex, int count, BuildContext context);
+typedef List<Widget> ListBuilder(BuildContext context, int startIndex, int count);
 
 class HomogeneousViewport extends RenderObjectWidget {
   HomogeneousViewport({
@@ -137,7 +137,7 @@ class HomogeneousViewportElement extends RenderObjectElement<HomogeneousViewport
     assert(_layoutItemCount != null);
     List<Widget> newWidgets;
     if (_layoutItemCount > 0)
-      newWidgets = widget.builder(_layoutFirstIndex, _layoutItemCount, this);
+      newWidgets = widget.builder(this, _layoutFirstIndex, _layoutItemCount);
     else
       newWidgets = <Widget>[];
     _children = updateChildren(_children, newWidgets);

packages/unit/test/fn3/coordinates_test.dart

+import 'package:sky/rendering.dart';
 import 'package:sky/src/fn3.dart';
 import 'package:test/test.dart';
 
@@ -9,7 +10,6 @@ void main() {
 
     Key keyA = new GlobalKey();
     Key keyB = new GlobalKey();
-    Key keyC = new GlobalKey();
 
     tester.pumpFrame(
       new Stack([
@@ -34,13 +34,13 @@ void main() {
       ])
     );
 
-    expect(tester.findElementByKey(keyA).renderObject.localToGlobal(const Point(0.0, 0.0)),
+    expect((tester.findElementByKey(keyA).renderObject as RenderBox).localToGlobal(const Point(0.0, 0.0)),
            equals(const Point(100.0, 100.0)));
 
-    expect(tester.findElementByKey(keyB).renderObject.localToGlobal(const Point(0.0, 0.0)),
+    expect((tester.findElementByKey(keyB).renderObject as RenderBox).localToGlobal(const Point(0.0, 0.0)),
            equals(const Point(100.0, 200.0)));
 
-    expect(tester.findElementByKey(keyB).renderObject.globalToLocal(const Point(110.0, 205.0)),
+    expect((tester.findElementByKey(keyB).renderObject as RenderBox).globalToLocal(const Point(110.0, 205.0)),
            equals(const Point(10.0, 5.0)));
   });
 }

packages/unit/test/fn3/homogeneous_viewport_test.dart

@@ -33,7 +33,7 @@ void main() {
 
     Widget builder() {
       return new TestComponent(new HomogeneousViewport(
-        builder: (int start, int count, BuildContext context) {
+        builder: (BuildContext context, int start, int count) {
           List<Widget> result = <Widget>[];
           for (int index = start; index < start + count; index += 1) {
             callbackTracker.add(index);
@@ -52,18 +52,19 @@ void main() {
 
     tester.pumpFrame(builder());
 
-    TestComponentState testComponent = tester.findElement((element) => element.widget is TestComponent).state;
+    StatefulComponentElement testComponent = tester.findElement((element) => element.widget is TestComponent);
+    TestComponentState testComponentState = testComponent.state;
 
     expect(callbackTracker, equals([0, 1, 2, 3, 4, 5]));
 
     callbackTracker.clear();
-    testComponent.go(false);
+    testComponentState.go(false);
     tester.pumpFrameWithoutChange();
 
     expect(callbackTracker, equals([]));
 
     callbackTracker.clear();
-    testComponent.go(true);
+    testComponentState.go(true);
     tester.pumpFrameWithoutChange();
 
     expect(callbackTracker, equals([0, 1, 2, 3, 4, 5]));
@@ -80,7 +81,7 @@ void main() {
 
     double offset = 300.0;
 
-    ListBuilder itemBuilder = (int start, int count, BuildContext context) {
+    ListBuilder itemBuilder = (BuildContext context, int start, int count) {
       List<Widget> result = <Widget>[];
       for (int index = start; index < start + count; index += 1) {
         callbackTracker.add(index);
@@ -130,7 +131,7 @@ void main() {
 
     double offset = 300.0;
 
-    ListBuilder itemBuilder = (int start, int count, BuildContext context) {
+    ListBuilder itemBuilder = (BuildContext context, int start, int count) {
       List<Widget> result = <Widget>[];
       for (int index = start; index < start + count; index += 1) {
         callbackTracker.add(index);

packages/unit/test/widget/block_test.dart

-import 'package:quiver/testing/async.dart';
 import 'package:sky/widgets.dart';
 import 'package:test/test.dart';