Make the stocks popup menu fade in

sky/sdk/lib/framework/rendering/box.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:math' as math;
 import 'dart:sky' as sky;
 import 'dart:typed_data';
 import 'object.dart';
 import '../painting/shadows.dart';
 import 'package:vector_math/vector_math.dart';
@@ skipping 421 matching lines @@
   void performLayout() {
     if (child != null) {
       child.layout(_getInnerConstraints(constraints));
       size = child.size;
     } else {
       performResize();
     }
   }
 }
 
+class RenderOpacity extends RenderProxyBox {
+  RenderOpacity({ RenderBox child, double opacity })
+    : this._opacity = opacity, super(child) {
+    assert(opacity >= 0.0 && opacity <= 1.0);
+  }
+
+  double _opacity;
+  double get opacity => _opacity;
+  void set opacity (double value) {
+    assert(value != null);
+    assert(value >= 0.0 && value <= 1.0);
+    if (_opacity == value)
+      return;
+    _opacity = value;
+    markNeedsPaint();
+  }
+
+  void paint(RenderObjectDisplayList canvas) {
+    if (child != null) {
+      if (_opacity == 0.0)
+        return;
+
+      if (_opacity == 1.0) {
+        child.paint(canvas);
+        return;
+      }
+
+      Paint paint = new Paint()
+        ..color = new Color.fromARGB((_opacity * 255).floor(), 0, 0, 0);
+        ..setTransferMode(sky.TransferMode.srcOverMode);
+      canvas.saveLayer(null, paint);
+      child.paint(canvas);
+      canvas.restore();
+    }
+  }
+}
+
 class RenderClipRect extends RenderProxyBox {
   RenderClipRect({ RenderBox child }) : super(child);
 
   void paint(RenderObjectDisplayList canvas) {
     if (child != null) {
       canvas.save();
       canvas.clipRect(new Rect.fromSize(size));
       child.paint(canvas);
       canvas.restore();
     }
@@ skipping 683 matching lines @@
 
   void defaultPaint(RenderObjectDisplayList canvas) {
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is ParentDataType);
       canvas.paintChild(child, child.parentData.position);
       child = child.parentData.nextSibling;
     }
   }
 }