Avoid drawing an extra row when the number of rows that fit on the screen is integral.

sky/sdk/lib/widgets/fixed_height_scrollable.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 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/scrollable.dart';
 
@@ skipping 43 matching lines @@
 
   Widget buildContent() {
     if (itemCount != _previousItemCount) {
       _previousItemCount = itemCount;
       _updateContentsHeight();
       _updateScrollOffset();
     }
 
     int itemShowIndex = 0;
     int itemShowCount = 0;
-
     double offsetY = 0.0;
-
     if (_height != null && _height > 0.0) {
       if (scrollOffset < 0.0) {
         double visibleHeight = _height + scrollOffset;
         itemShowCount = (visibleHeight / itemHeight).round() + 1;
         offsetY = scrollOffset;
       } else {
-        itemShowCount = (_height / itemHeight).ceil() + 1;
+        itemShowCount = (_height / itemHeight).ceil();
         double alignmentDelta = -scrollOffset % itemHeight;
-        if (alignmentDelta != 0.0)
+        double drawStart;
+        if (alignmentDelta != 0.0) {
           alignmentDelta -= itemHeight;
-
-        double drawStart = scrollOffset + alignmentDelta;
+          itemShowCount += 1;
+          drawStart = scrollOffset + alignmentDelta;
+          offsetY = -alignmentDelta;
+        } else {
+          drawStart = scrollOffset;
+        }
         itemShowIndex = math.max(0, (drawStart / itemHeight).floor());
-
-        offsetY = -alignmentDelta;
       }
     }
 
     List<Widget> items = buildItems(itemShowIndex, itemShowCount);
     assert(items.every((item) => item.key != null));
 
     // TODO(ianh): Refactor this so that it does the building in the
     // same frame as the size observing, similar to BlockViewport, but
     // keeping the fixed-height optimisations.
     return new SizeObserver(
       callback: _handleSizeChanged,
       child: new Viewport(
         offset: offsetY,
         child: new Container(
           padding: padding,
           child: new Block(items)
         )
       )
     );
   }
 
   List<Widget> buildItems(int start, int count);
 
 }