Cleanup of SkyBinding, and resultant yak shaving.

sky/sdk/lib/widgets/widget.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
 import 'dart:sky' as sky;
 
+import '../base/hit_test.dart';
 import '../rendering/box.dart';
 import '../rendering/object.dart';
 import '../rendering/sky_binding.dart';
 
 export '../rendering/box.dart' show BoxConstraints, BoxDecoration, Border, BorderSide, EdgeDims;
 export '../rendering/flex.dart' show FlexDirection;
 export '../rendering/object.dart' show Point, Size, Rect, Color, Paint, Path;
 
 final bool _shouldLogRenderDuration = false;
 
@@ skipping 478 matching lines @@
     // TODO(abarth): We should split RenderObjectWrapper into two pieces so that
     //               RenderViewObject doesn't need to inherit all this code it
     //               doesn't need.
     assert(parent != null || this is RenderViewWrapper);
     if (old == null) {
       _root = createNode();
       _ancestor = findAncestor(RenderObjectWrapper);
       if (_ancestor is RenderObjectWrapper)
         _ancestor.insertChildRoot(this, slot);
     } else {
+      assert(old is RenderObjectWrapper);
       _root = old.root;
       _ancestor = old._ancestor;
     }
     assert(_root == root); // in case a subclass reintroduces it
     assert(root != null);
     assert(mounted);
     _nodeMap[root] = this;
     syncRenderObject(old);
   }
 
@@ skipping 259 matching lines @@
     }
 
     assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
 }
 
 class WidgetSkyBinding extends SkyBinding {
 
   WidgetSkyBinding({ RenderView renderViewOverride: null })
-      : super(renderViewOverride: renderViewOverride) {
-    assert(_skyBinding == null);
-  }
+      : super(renderViewOverride: renderViewOverride);
 
-  static WidgetSkyBinding _skyBinding;
-  static SkyBinding get skyBinding => _skyBinding;
   static void initWidgetSkyBinding({ RenderView renderViewOverride: null }) {
-    if (_skyBinding == null)
-      _skyBinding = new WidgetSkyBinding(renderViewOverride: renderViewOverride);
+    if (SkyBinding.instance == null)
+      new WidgetSkyBinding(renderViewOverride: renderViewOverride);
+    assert(SkyBinding.instance is WidgetSkyBinding);
   }
 
   void dispatchEvent(sky.Event event, HitTestResult result) {
-    assert(_skyBinding == this);
+    assert(SkyBinding.instance == this);
     super.dispatchEvent(event, result);
     for (HitTestEntry entry in result.path.reversed) {
       Widget target = RenderObjectWrapper._getMounted(entry.target);
       if (target == null)
         continue;
       RenderObject targetRoot = target.root;
       while (target != null && target.root == targetRoot) {
         if (target is Listener)
           target._handleEvent(event);
         target = target._parent;
@@ skipping 24 matching lines @@
     assert(_dirty);
     assert(_mounted);
     assert(parent == null);
     _sync(null, null);
   }
 
 }
 
 class RenderViewWrapper extends OneChildRenderObjectWrapper {
   RenderViewWrapper({ String key, Widget child }) : super(key: key, child: child);
-
   RenderView get root => super.root;
-  RenderView createNode() => WidgetSkyBinding._skyBinding.renderView;
+  RenderView createNode() => SkyBinding.instance.renderView;
 }
 
 class AppContainer extends AbstractWidgetRoot {
-  AppContainer(this.app);
-
+  AppContainer(this.app) {
+    assert(SkyBinding.instance is WidgetSkyBinding);
+  }
   final App app;
-
   Widget build() => new RenderViewWrapper(child: app);
 }
 
 void runApp(App app, { RenderView renderViewOverride }) {
   WidgetSkyBinding.initWidgetSkyBinding(renderViewOverride: renderViewOverride);
   new AppContainer(app);
 }
 
 typedef Widget Builder();
 
@@ skipping 30 matching lines @@
     if (root.parent == null) {
       // we haven't attached it yet
       assert(_container.child == null);
       _container.child = root;
     }
     assert(root.parent == _container);
   }
 
   Widget build() => builder();
 }