Rename and refactor ScrollView hierarchy (#7865)

This prepares us for a CustomScrollView that takes slivers.
diff --git a/examples/flutter_gallery/lib/demo/cards_demo.dart b/examples/flutter_gallery/lib/demo/cards_demo.dart
index a7167d7..fb1e9e9 100644
--- a/examples/flutter_gallery/lib/demo/cards_demo.dart
+++ b/examples/flutter_gallery/lib/demo/cards_demo.dart
@@ -134,7 +134,7 @@
       appBar: new AppBar(
         title: new Text('Travel stream')
       ),
-      body: new ScrollView(
+      body: new ListView(
         itemExtent: TravelDestinationItem.height,
         padding: const EdgeInsets.only(top: 8.0, left: 8.0, right: 8.0),
         children: destinations.map((TravelDestination destination) {