Fix Observatory virtual-collection layout issues

runtime/observatory/lib/src/elements/persistent_handles.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library persitent_handles_page;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/src/elements/containers/virtual_collection.dart';
@@ skipping 168 matching lines @@
         ..text = '0B',
       new SpanElement()
         ..classes = ['peer']
         ..text = '0x00000',
       new SpanElement()..classes = ['object'],
       new SpanElement()
         ..classes = ['finalizer']
         ..text = 'dart::Class::Method()'
     ];
 
-  Element _createWeakHeader() => new DivElement()
-    ..classes = ['weak-item']
-    ..children = [
-      _createHeaderButton(const ['external-size'], 'External Size',
-          _SortingField.externalSize, _SortingDirection.descending),
-      _createHeaderButton(const ['peer'], 'Peer', _SortingField.peer,
-          _SortingDirection.descending),
-      new SpanElement()
-        ..classes = ['object']
-        ..text = 'Object',
-      _createHeaderButton(const ['finalizer'], 'Finalizer Callback',
-          _SortingField.finalizerCallback, _SortingDirection.ascending)
-    ];
+  List<HtmlElement> _createWeakHeader() => [
+        new DivElement()
+          ..classes = ['weak-item']
+          ..children = [
+            _createHeaderButton(const ['external-size'], 'External Size',
+                _SortingField.externalSize, _SortingDirection.descending),
+            _createHeaderButton(const ['peer'], 'Peer', _SortingField.peer,
+                _SortingDirection.descending),
+            new SpanElement()
+              ..classes = ['object']
+              ..text = 'Object',
+            _createHeaderButton(const ['finalizer'], 'Finalizer Callback',
+                _SortingField.finalizerCallback, _SortingDirection.ascending)
+          ]
+      ];
 
   ButtonElement _createHeaderButton(List<String> classes, String text,
           _SortingField field, _SortingDirection direction) =>
       new ButtonElement()
         ..classes = classes
         ..text = _sortingField != field
             ? text
             : _sortingDirection == _SortingDirection.ascending
                 ? '$text▼'
                 : '$text▲'
@@ skipping 38 matching lines @@
     _r.dirty();
     _handles = await _repository.get(_isolate);
     _r.dirty();
   }
 
   static int _getExternalSize(M.WeakPersistentHandle h) => h.externalSize;
   static String _getPeer(M.WeakPersistentHandle h) => h.peer;
   static String _getFinalizerCallback(M.WeakPersistentHandle h) =>
       '${h.callbackSymbolName} (${h.callbackAddress})';
 }