Support getting baseline from paint as well as layout.

sky/sdk/lib/rendering/box.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:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 
 import '../base/debug.dart';
@@ skipping 288 matching lines @@
   }
   // getDistanceToBaseline() returns the distance from the
   // y-coordinate of the position of the box to the y-coordinate of
   // the first given baseline in the box's contents. This is used by
   // certain layout models to align adjacent boxes on a common
   // baseline, regardless of padding, font size differences, etc. If
   // there is no baseline, then it returns the distance from the
   // y-coordinate of the position of the box to the y-coordinate of
   // the bottom of the box, i.e., the height of the box. Only call
   // this after layout has been performed. You are only allowed to
-  // call this from the parent of this node, and only during
-  // that parent's performLayout().
+  // call this from the parent of this node during that parent's
+  // performLayout() or paint().
   double getDistanceToBaseline(TextBaseline baseline) {
     assert(!needsLayout);
     assert(!_debugDoingBaseline);
     final parent = this.parent; // TODO(ianh): Remove this once the analyzer is cleverer
     assert(parent is RenderObject);
-    assert(parent == RenderObject.debugActiveLayout);
-    assert(parent.debugDoingThisLayout);
+    assert(() {
+      if (RenderObject.debugDoingLayout)
+        return (parent == RenderObject.debugActiveLayout) && parent.debugDoingThisLayout;
+      if (RenderObject.debugDoingPaint)
+        return (parent == RenderObject.debugActivePaint) && parent.debugDoingThisPaint;
+      return false;
+    });
     assert(_debugSetDoingBaseline(true));
     double result = getDistanceToActualBaseline(baseline);
     assert(_debugSetDoingBaseline(false));
     assert(parent == this.parent); // TODO(ianh): Remove this once the analyzer is cleverer
     if (result == null)
       return size.height;
     return result;
   }
   // getDistanceToActualBaseline() must only be called from
   // getDistanceToBaseline() and computeDistanceToActualBaseline(). Do
@@ skipping 1110 matching lines @@
 
   void defaultPaint(PaintingCanvas canvas, Offset offset) {
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is ParentDataType);
       canvas.paintChild(child, child.parentData.position + offset);
       child = child.parentData.nextSibling;
     }
   }
 }