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

sky/sdk/lib/base/debug.dart

Index: sky/sdk/lib/base/debug.dart
diff --git a/sky/sdk/lib/base/debug.dart b/sky/sdk/lib/base/debug.dart
index f8d8160b2cc25a3e7d5147741f340bc39bd1a42d..e0dcf0cebd0e6123cfc9ed343fd726b48eec5283 100644
--- a/sky/sdk/lib/base/debug.dart
+++ b/sky/sdk/lib/base/debug.dart
@@ -2,6 +2,8 @@
 // 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() {
@@ -13,3 +15,12 @@ bool _initInDebugBuild() {
   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;