Make the drawer, popup menus, dialogs, and settings page scrollable.

sky/sdk/lib/widgets/basic.dart

Index: sky/sdk/lib/widgets/basic.dart
diff --git a/sky/sdk/lib/widgets/basic.dart b/sky/sdk/lib/widgets/basic.dart
index f618099d87c59312c980dac28e12e9a7da625d05..48fa771a931c6b49db02e24023a8a310b1fa42b8 100644
--- a/sky/sdk/lib/widgets/basic.dart
+++ b/sky/sdk/lib/widgets/basic.dart
@@ -281,6 +281,26 @@ class Baseline extends OneChildRenderObjectWrapper {
 
 }
 
+class Viewport extends OneChildRenderObjectWrapper {
+
+  Viewport({
+    String key,
+    this.offset: 0.0,
+    Widget child
+  }) : super(key: key, child: child);
+
+  final double offset;
+
+  RenderViewport get root => super.root;
+  RenderViewport createNode() => new RenderViewport(scrollOffset: new Offset(0.0, offset));
+
+  void syncRenderObject(Viewport old) {
+    super.syncRenderObject(old);
+    root.scrollOffset = new Offset(0.0, offset);
+  }
+
+}
+
 class SizeObserver extends OneChildRenderObjectWrapper {
 
   SizeObserver({ String key, this.callback, Widget child })