Provide some debug-mode time hooks to visually debug painting and layout.

sky/engine/core/painting/Rect.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.
 
 part of dart.sky;
 
 /// Holds 4 floating-point coordinates for a rectangle.
 class Rect {
   Rect();
 
@@ skipping 12 matching lines @@
       ..[2] = left + width
       ..[3] = top + height;
   }
 
   final Float32List _value = new Float32List(4);
   double get left => _value[0];
   double get top => _value[1];
   double get right => _value[2];
   double get bottom => _value[3];
 
+  Rect shift(Offset offset) {
+    return new Rect.fromLTRB(left + offset.dx, top + offset.dy, right + offset.dx, bottom + offset.dy);
+  }
+  Rect inflate(double delta) {
+    return new Rect.fromLTRB(left - delta, top - delta, right + delta, bottom + delta);
+  }
+
   double get width => right - left;
   double get height => bottom - top;
 
   Size get size => new Size(width, height);
 
   double get shortestSide {
     double w = width.abs();
     double h = height.abs();
     return w < h ? w : h;
   }
@@ skipping 15 matching lines @@
       return false;
     for (var i = 0; i < 4; ++i) {
       if (_value[i] != other._value[i])
         return false;
     }
     return true;
   }
   int get hashCode =>_value.fold(373, (value, item) => (37 * value + item.hashCode));
   String toString() => "Rect.fromLTRB($left, $top, $right, $bottom)";
 }