Move VariableHeightScrollable to sdk/lib/widgets

sky/sdk/example/widgets/card_collection.dart

Index: sky/sdk/example/widgets/card_collection.dart
diff --git a/sky/sdk/example/widgets/card_collection.dart b/sky/sdk/example/widgets/card_collection.dart
index e20648c21fe46294808986c7ebb01127763a15fc..d84ee8663ae2af9be3e2406523667ea4f9cf56c3 100644
--- a/sky/sdk/example/widgets/card_collection.dart
+++ b/sky/sdk/example/widgets/card_collection.dart
@@ -6,16 +6,14 @@ import 'dart:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 import 'package:sky/animation/animation_performance.dart';
-import 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/base/lerp.dart';
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/theme/colors.dart';
 import 'package:sky/widgets/animated_container.dart';
 import 'package:sky/widgets/basic.dart';
-import 'package:sky/widgets/block_viewport.dart';
 import 'package:sky/widgets/card.dart';
 import 'package:sky/widgets/scaffold.dart';
-import 'package:sky/widgets/scrollable.dart';
+import 'package:sky/widgets/variable_height_scrollable.dart';
 import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/tool_bar.dart';
 import 'package:sky/widgets/widget.dart';
@@ -26,44 +24,6 @@ const double _kMinFlingVelocity = 700.0;
 const double _kMinFlingVelocityDelta = 400.0;
 const double _kDismissCardThreshold = 0.6;
 
-class VariableHeightScrollable extends Scrollable {
-  VariableHeightScrollable({
-    String key,
-    this.builder,
-    this.token
-  }) : super(key: key);
-
-  IndexedBuilder builder;
-  Object token;
-
-  void syncFields(VariableHeightScrollable source) {
-    builder = source.builder;
-    token = source.token;
-    super.syncFields(source);
-  }
-
-  ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
-  OverscrollBehavior get scrollBehavior => super.scrollBehavior;
-
-  void _handleSizeChanged(Size newSize) {
-    setState(() {
-      scrollBehavior.containerHeight = newSize.height;
-      scrollBehavior.contentsHeight = 5000.0;
-    });
-  }
-
-  Widget buildContent() {
-    return new SizeObserver(
-      callback: _handleSizeChanged,
-      child: new BlockViewport(
-        builder: builder,
-        startOffset: scrollOffset,
-        token: token
-      )
-    );
-  }
-}
-
 class CardCollectionApp extends App {
 
   final TextStyle cardLabelStyle =
@@ -72,6 +32,7 @@ class CardCollectionApp extends App {
   final List<double> cardHeights = [
     48.0, 64.0, 82.0, 46.0, 60.0, 55.0, 84.0, 96.0, 50.0, 
     48.0, 64.0, 82.0, 46.0, 60.0, 55.0, 84.0, 96.0, 50.0,
+    48.0, 64.0, 82.0, 46.0, 60.0, 55.0, 84.0, 96.0, 50.0,
     48.0, 64.0, 82.0, 46.0, 60.0, 55.0, 84.0, 96.0, 50.0
   ];
 
@@ -214,7 +175,8 @@ class CardCollectionApp extends App {
       decoration: new BoxDecoration(backgroundColor: Theme.of(this).primarySwatch[50]),
       child: new VariableHeightScrollable(
         builder: _builder,
-        token: visibleCardIndices.length
+        token: visibleCardIndices.length,
+        itemCount: visibleCardIndices.length
       )
     );