Fix bugs found by Dart analyzer

sky/sdk/example/raw/baseline.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;
 
 void drawText(sky.Canvas canvas, String lh) {
   sky.Paint paint = new sky.Paint();
 
   // offset down
@@ skipping 20 matching lines @@
   sky.Path path = new sky.Path();
   path.moveTo(0.0, 0.0);
   path.lineTo(block.maxContentWidth, 0.0);
   path.moveTo(0.0, block.alphabeticBaseline);
   path.lineTo(block.maxContentWidth, block.alphabeticBaseline);
   path.moveTo(0.0, block.height);
   path.lineTo(block.maxContentWidth, block.height);
   paint.color = const sky.Color(0xFFFF9000);
   paint.setStyle(sky.PaintingStyle.stroke);
   paint.strokeWidth = 3.0;
-  canvas.drawPath(path, paint);  
+  canvas.drawPath(path, paint);
 
   // paint the text
   layoutRoot.paint(canvas);
 }
 
 void main() {
   // prepare the rendering
   sky.PictureRecorder recorder = new sky.PictureRecorder();
-  sky.Canvas canvas = new sky.Canvas(recorder, new sky.Size(sky.view.width, sky.view.height));
+  sky.Canvas canvas = new sky.Canvas(recorder, new sky.Rect.fromLTWH(0.0, 0.0, sky.view.width, sky.view.height));
 
   // background
   sky.Paint paint = new sky.Paint();
   paint.color = const sky.Color(0xFFFFFFFF);
   paint.setStyle(sky.PaintingStyle.fill);
   canvas.drawRect(new sky.Rect.fromLTRB(0.0, 0.0, sky.view.width, sky.view.height), paint);
 
   canvas.translate(10.0, 0.0);
   drawText(canvas, '1.0');
   drawText(canvas, 'lh');
 
   // put it on the screen
   sky.view.picture = recorder.endRecording();
   sky.view.scheduleFrame();
 }