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

sky/sdk/lib/base/debug.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;
+
 final bool inDebugBuild = _initInDebugBuild();
 
 bool _initInDebugBuild() {
   bool _inDebug = false;
   bool setAssert() {
     _inDebug = true;
     return true;
   }
   assert(setAssert());
   return _inDebug;
 }
+
+bool debugPaintSizeEnabled = false;
+const sky.Color debugPaintSizeColor = const sky.Color(0xFF00FFFF);
+
+bool debugPaintBaselinesEnabled = false;
+const sky.Color debugPaintAlphabeticBaselineColor = const sky.Color(0xFF00FF00);
+const sky.Color debugPaintIdeographicBaselineColor = const sky.Color(0xFFFFD000);
+
+bool debugPaintBoundsEnabled = false;