Improve drawer performance

sky/sdk/lib/widgets/drawer_item.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:sky' as sky;
 
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/button_base.dart';
@@ skipping 28 matching lines @@
   }
 
   Color _getBackgroundColor(ThemeData themeData) {
     if (highlight)
       return themeData.highlightColor;
     if (selected)
       return themeData.selectedColor;
     return colors.transparent;
   }
 
+  sky.ColorFilter _getColorFilter(ThemeData themeData) {
+    if (selected)
+      return new sky.ColorFilter.mode(themeData.primaryColor, sky.TransferMode.srcATop);
+    return new sky.ColorFilter.mode(const Color(0x73000000), sky.TransferMode.dstIn);
+  }
+
   Widget buildContent() {
     ThemeData themeData = Theme.of(this);
 
     List<Widget> flexChildren = new List<Widget>();
     if (icon != null) {
-      Widget child = new Icon(type: icon, size: 24);
-      if (selected) {
-        child = new ColorFilter(
-          color: themeData.primaryColor,
-          transferMode: sky.TransferMode.srcATop,
-          child: child
-        );
-      }
       flexChildren.add(
-        new Opacity(
-          opacity: selected ? 1.0 : 0.45,
-          child: new Padding(
-            padding: const EdgeDims.symmetric(horizontal: 16.0),
-            child: child
-          )
+        new Padding(
+          padding: const EdgeDims.symmetric(horizontal: 16.0),
+          child: new Icon(
+            type: icon,
+            size: 24,
+            colorFilter: _getColorFilter(themeData))
         )
       );
     }
     flexChildren.add(
       new Flexible(
         child: new Padding(
           padding: const EdgeDims.symmetric(horizontal: 16.0),
           child: new DefaultTextStyle(
             style: _getTextStyle(themeData),
             child: new Flex(children, direction: FlexDirection.horizontal)
@@ skipping 10 matching lines @@
       child: new Container(
         height: 48.0,
         decoration: new BoxDecoration(backgroundColor: _getBackgroundColor(themeData)),
         child: new InkWell(
           child: new Flex(flexChildren)
         )
       )
     );
   }
 }