Add Canvas.drawPicture

sky/engine/core/painting/Canvas.idl

 // 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.
 
 // TODO(mpcomplete): Figure out a better SkMatrix/SkRect representation.
 interface Canvas {
   // Height and width are used for culling optimizations and do not necessarily
   // imply that the Canvas is backed by a buffer with any specific bounds.
   readonly attribute float height;
   readonly attribute float width;
 
   void save();
   void saveLayer(float[] bounds4 /* optional */, Paint paint /* optional */);
   void restore();
 
   void translate(float dx, float dy);
   void scale(float sx, float sy);
   void rotateDegrees(float degrees);
   void skew(float sx, float sy);
   void concat(float[] matrix9);
 
   void clipRect(float[] rect4);
 
+  void drawPicture(Picture picture);
+
   void drawPaint(Paint paint);
   void drawRect(float[] rect4, Paint paint);
   void drawOval(float[] rect4, Paint paint);
   void drawCircle(float x, float y, float radius, Paint paint);
 };