Minor optimisations and cleanup to the text rendering stuff.

sky/sdk/lib/rendering/paragraph.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;
 
 import 'box.dart';
 import 'object.dart';
 import '../painting/text_style.dart';
 
@@ skipping 85 matching lines @@
 class RenderParagraph extends RenderBox {
 
   RenderParagraph(InlineBase inlineValue) {
     _layoutRoot.rootElement = _document.createElement('p');
     inline = inlineValue;
   }
 
   final sky.Document _document = new sky.Document();
   final sky.LayoutRoot _layoutRoot = new sky.LayoutRoot();
 
+  BoxConstraints _constraintsForCurrentLayout; // when null, we don't have a current layout
+
   InlineBase _inline;
-  BoxConstraints _constraintsForCurrentLayout;
-
   InlineBase get inline => _inline;
   void set inline (InlineBase value) {
     if (_inline == value)
       return;
     _inline = value;
     _layoutRoot.rootElement.setChild(_inline._toDOM(_document));
+    _constraintsForCurrentLayout = null;
     markNeedsLayout();
   }
 
   void _layout(BoxConstraints constraints) {
+    assert(constraints != null);
+    if (_constraintsForCurrentLayout == constraints)
+      return; // already cached this layout
     _layoutRoot.maxWidth = constraints.maxWidth;
     _layoutRoot.minWidth = constraints.minWidth;
     _layoutRoot.minHeight = constraints.minHeight;
     _layoutRoot.maxHeight = constraints.maxHeight;
     _layoutRoot.layout();
     _constraintsForCurrentLayout = constraints;
   }
 
   double getMinIntrinsicWidth(BoxConstraints constraints) {
     _layout(constraints);
@@ skipping 30 matching lines @@
   }
 
   void paint(RenderCanvas canvas) {
     // Ideally we could compute the min/max intrinsic width/height with a
     // non-destructive operation. However, currently, computing these values
     // will destroy state inside the layout root. If that happens, we need to
     // get back the correct state by calling _layout again.
     //
     // TODO(abarth): Make computing the min/max intrinsic width/height a
     //               non-destructive operation.
-    if (_constraintsForCurrentLayout != constraints && constraints != null)
-      _layout(constraints);
-
+    _layout(constraints);
     _layoutRoot.paint(canvas);
   }
 
   // we should probably expose a way to do precise (inter-glpyh) hit testing
 
   String debugDescribeSettings(String prefix) {
     String result = '${super.debugDescribeSettings(prefix)}';
     result += '${prefix}inline:\n${inline.toString("$prefix  ")}\n';
     return result;
   }
 }