Replace BoxDimensions with sky.Size

sky/examples/raw/render_paragraph.dart

Index: sky/examples/raw/render_paragraph.dart
diff --git a/sky/examples/raw/render_paragraph.dart b/sky/examples/raw/render_paragraph.dart
index 32d6eebc4d017620dcd560f4b2c90acea76e290e..f2e444d4a8043bf64d1171b8f1319161b23fe119 100644
--- a/sky/examples/raw/render_paragraph.dart
+++ b/sky/examples/raw/render_paragraph.dart
@@ -16,10 +16,8 @@ class RenderSolidColor extends RenderDecoratedBox {
       : backgroundColor = backgroundColor,
         super(new BoxDecoration(backgroundColor: backgroundColor));
 
-  BoxDimensions getIntrinsicDimensions(BoxConstraints constraints) {
-    return new BoxDimensions.withConstraints(constraints,
-                                             height: desiredHeight,
-                                             width: desiredWidth);
+  Size getIntrinsicDimensions(BoxConstraints constraints) {
+    return constraints.constrain(new Size(desiredWidth, desiredHeight));
   }
 
   void performLayout() {