Sky: Small fixes to Gradient interface. Added comments and renamed constructors.

sky/sdk/lib/framework/painting/box_painter.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 'dart:sky' show Point, Size, Rect, Color, Paint, Path;
 import 'shadows.dart';
 
 class BorderSide {
   const BorderSide({
@@ skipping 67 matching lines @@
     this.endPoints,
     this.colors,
     this.colorStops,
     this.tileMode: sky.TileMode.clamp
   });
 
   String toString() =>
       'LinearGradient($endPoints, $colors, $colorStops, $tileMode)';
 
   sky.Shader createShader() {
-    return new sky.Gradient.Linear(this.endPoints, this.colors, this.colorStops,
+    return new sky.Gradient.linear(this.endPoints, this.colors, this.colorStops,
                                    this.tileMode);
   }
 
   final List<Point> endPoints;
   final List<Color> colors;
   final List<double> colorStops;
   final sky.TileMode tileMode;
 }
 
 class RadialGradient extends Gradient {
   RadialGradient({
     this.center,
     this.radius,
     this.colors,
     this.colorStops,
     this.tileMode: sky.TileMode.clamp
   });
 
   String toString() =>
       'RadialGradient($center, $radius, $colors, $colorStops, $tileMode)';
 
   sky.Shader createShader() {
-    return new sky.Gradient.Radial(this.center, this.radius, this.colors,
+    return new sky.Gradient.radial(this.center, this.radius, this.colors,
                                    this.colorStops, this.tileMode);
   }
 
   final Point center;
   final double radius;
   final List<Color> colors;
   final List<double> colorStops;
   final sky.TileMode tileMode;
 }
 
@@ skipping 121 matching lines @@
       path = new Path();
       path.moveTo(rect.left, rect.bottom);
       path.lineTo(rect.left + _decoration.border.left.width, rect.bottom - _decoration.border.bottom.width);
       path.lineTo(rect.left + _decoration.border.left.width, rect.top + _decoration.border.top.width);
       path.lineTo(rect.left, rect.top);
       path.close();
       canvas.drawPath(path, paint);
     }
   }
 }