Simplify TabView API

Instead of taking a builder and a generic type, we can just take a
List<Widget>.

examples/material_gallery/lib/demo/page_selector_demo.dart

@@ -85,9 +85,8 @@ class TabViewDemo extends StatelessComponent {
               )
             ),
             new Flexible(
-              child: new TabBarView<String>(
-                items: _iconNames,
-                itemBuilder: _buildTabView
+              child: new TabBarView(
+                children: _iconNames.map(_buildTabView).toList()
               )
             )
           ]);

examples/material_gallery/lib/demo/tabs_demo.dart

@@ -27,9 +27,8 @@ class TabsDemo extends StatefulComponent {
 
 class _TabsDemoState extends State<TabsDemo> {
   Widget build(_) {
-    return new TabBarView<String>(
-      items: _iconNames,
-      itemBuilder: (String iconName) {
+    return new TabBarView(
+      children: _iconNames.map((String iconName) {
         return new Container(
           key: new ValueKey<String>(iconName),
           padding: const EdgeDims.all(12.0),
@@ -37,7 +36,7 @@ class _TabsDemoState extends State<TabsDemo> {
             child: new Center(child: new Icon(icon: "action/$iconName", size:IconSize.s48))
           )
         );
-      }
+      }).toList()
     );
   }
 }

examples/stocks/lib/stock_home.dart

@@ -267,18 +267,11 @@ class StockHomeState extends State<StockHome> {
         toolBar: _isSearching ? buildSearchBar() : buildToolBar(),
         floatingActionButton: buildFloatingActionButton(),
         drawer: _buildDrawer(context),
-        body: new TabBarView<StockHomeTab>(
-          items: <StockHomeTab>[StockHomeTab.market, StockHomeTab.portfolio],
-          itemBuilder: (StockHomeTab tab) {
-            switch (tab) {
-              case StockHomeTab.market:
-                return _buildStockTab(context, tab, config.symbols);
-              case StockHomeTab.portfolio:
-                return _buildStockTab(context, tab, portfolioSymbols);
-              default:
-                assert(false);
-            }
-          }
+        body: new TabBarView(
+          children: <Widget>[
+            _buildStockTab(context, StockHomeTab.market, config.symbols),
+            _buildStockTab(context, StockHomeTab.portfolio, portfolioSymbols),
+          ]
         )
       )
     );

packages/flutter/lib/src/material/tabs.dart

@@ -764,36 +764,29 @@ class _TabBarState<T> extends ScrollableState<TabBar<T>> implements TabBarSelect
   }
 }
 
-typedef Widget TabItemBuilder<T>(T item);
-
-class TabBarView<T> extends PageableList {
+class TabBarView extends PageableList {
   TabBarView({
     Key key,
-    List<T> items,
-    TabItemBuilder<T> itemBuilder
-  }) : items = items, itemBuilder = itemBuilder, super(
+    List<Widget> children
+  }) : super(
     key: key,
     scrollDirection: ScrollDirection.horizontal,
-    children: items.map((T item) => itemBuilder(item)).toList(),
-    itemsWrap: false
+    children: children
   ) {
-    assert(items != null);
-    assert(items.length > 1);
+    assert(children != null);
+    assert(children.length > 1);
   }
 
-  final List<T> items;
-  final TabItemBuilder<T> itemBuilder;
-
-  _TabBarViewState createState() => new _TabBarViewState<T>();
+  _TabBarViewState createState() => new _TabBarViewState();
 }
 
-class _TabBarViewState<T> extends PageableListState<TabBarView<T>> implements TabBarSelectionPerformanceListener {
+class _TabBarViewState extends PageableListState<TabBarView> implements TabBarSelectionPerformanceListener {
 
   TabBarSelectionState _selection;
   List<Widget> _items;
   AnimationDirection _scrollDirection = AnimationDirection.forward;
 
-  int get _tabCount => config.items.length;
+  int get _tabCount => config.children.length;
 
   BoundedBehavior _boundedBehavior;
 
@@ -802,7 +795,7 @@ class _TabBarViewState<T> extends PageableListState<TabBarView<T>> implements Ta
     return _boundedBehavior;
   }
 
-  void _initSelection(TabBarSelectionState<T> selection) {
+  void _initSelection(TabBarSelectionState selection) {
     _selection = selection;
     if (_selection != null) {
       _selection.registerPerformanceListener(this);
@@ -919,7 +912,7 @@ class _TabBarViewState<T> extends PageableListState<TabBarView<T>> implements Ta
   }
 
   Widget buildContent(BuildContext context) {
-    TabBarSelectionState<T> newSelection = TabBarSelection.of(context);
+    TabBarSelectionState newSelection = TabBarSelection.of(context);
     if (_selection != newSelection)
       _initSelection(newSelection);
     return new PageViewport(

packages/flutter/lib/src/widgets/scrollable_list.dart

@@ -41,10 +41,10 @@ class ScrollableList extends Scrollable {
   final ScrollableListPainter scrollableListPainter;
   final Iterable<Widget> children;
 
-  ScrollableState createState() => new _ScrollableList2State();
+  ScrollableState createState() => new _ScrollableListState();
 }
 
-class _ScrollableList2State extends ScrollableState<ScrollableList> {
+class _ScrollableListState extends ScrollableState<ScrollableList> {
   ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
   ExtentScrollBehavior get scrollBehavior => super.scrollBehavior;