Random cleanup of various Dart things in our tree.

sky/sdk/example/raw/hello_world.dart

Index: sky/sdk/example/raw/hello_world.dart
diff --git a/sky/sdk/example/raw/hello_world.dart b/sky/sdk/example/raw/hello_world.dart
index 9dc7b448decc002620692b1c69ea8e8c8292d28f..e667391734b3dcfd9f595a90d706ab33c6d84b98 100644
--- a/sky/sdk/example/raw/hello_world.dart
+++ b/sky/sdk/example/raw/hello_world.dart
@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import "dart:math";
 import 'dart:sky';
 
 Picture draw(int a, int r, int g, int b) {
@@ -13,7 +12,7 @@ Picture draw(int a, int r, int g, int b) {
   double radius = size.shortestSide * 0.45;
 
   Paint paint = new Paint()..color = new Color.fromARGB(a, r, g, b);
-  canvas.drawCircle(size.center, radius, paint);
+  canvas.drawCircle(size.center(Point.origin), radius, paint);
   return recorder.endRecording();
 }