Improve RenderNode performance

sky/sdk/lib/framework/rendering/render_node.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 '../node.dart';
+import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 class ParentData {
   void detach() {
     detachSiblings();
   }
   void detachSiblings() { } // workaround for lack of inter-class mixins in Dart
   void merge(ParentData other) {
     // override this in subclasses to merge in data from other into this
     assert(other.runtimeType == this.runtimeType);
   }
 }
 
 const kLayoutDirections = 4;
 
 double clamp({double min: 0.0, double value: 0.0, double max: double.INFINITY}) {
   assert(min != null);
   assert(value != null);
   assert(max != null);
-
-  if (value > max)
-    value = max;
-  if (value < min)
-    value = min;
-  return value;
+  return math.max(min, math.min(max, value));
 }
 
 class RenderNodeDisplayList extends sky.PictureRecorder {
   RenderNodeDisplayList(double width, double height) : super(width, height);
   void paintChild(RenderNode child, sky.Point position) {
-    save();
     translate(position.x, position.y);
     child.paint(this);
-    restore();
+    translate(-position.x, -position.y);
   }
 }
 
 abstract class RenderNode extends AbstractNode {
 
   // LAYOUT
 
   // parentData is only for use by the RenderNode that actually lays this
   // node out, and any other nodes who happen to know exactly what
   // kind of node that is.
@@ skipping 331 matching lines @@
     }
   }
 
   ChildType get firstChild => _firstChild;
   ChildType get lastChild => _lastChild;
   ChildType childAfter(ChildType child) {
     assert(child.parentData is ParentDataType);
     return child.parentData.nextSibling;
   }
 }