Remove race condition in Observatory memory page

runtime/observatory/lib/src/elements/memory/graph.dart

 // Copyright (c) 2017, 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.
 
 /// This Element is part of MemoryDashboardElement.
 ///
 /// The Element periodically interrogates the VM to log the memory usage of each
 /// Isolate and of the Native Memory.
 ///
 /// For each isolate it is shown the Used and Free heap (new and old are merged
@@ skipping 151 matching lines @@
     final config = new ChartConfig([sMemory], [0])
       ..legend = new ChartLegend(legend)
       ..registerDimensionAxis(0, axisConfig);
     config.minimumSize = new Rect(rect.width, rect.height);
     final data = new ChartData(columns, rows);
     final state = new ChartState(isMultiSelect: true)
       ..changes.listen(_handleEvent);
     final area = new CartesianArea(host, data, config, state: state)
       ..theme = theme;
     area.addChartBehavior(new Hovercard(builder: (int column, int row) {
+      final data = rows[row];
       if (column == 1) {
-        return _formatNativeOvercard(row);
+        return _formatNativeOvercard(data[1]);
       }
-      return _formatIsolateOvercard(_seenIsolates[column - 2].id, row);
+      final isolate = _seenIsolates[column - 2];
+      final index = _isolateIndex[isolate.id] * 2 + 2;
+      return _formatIsolateOvercard(isolate.name, data[index], data[index + 1]);
     }));
     area.draw();
 
     if (_selected != null) {
       state.select(_selected);
       if (_selected > 1) {
         state.select(_selected + 1);
       }
     }
   }
@@ skipping 129 matching lines @@
     final index = _isolateIndex[isolateId];
     final name = _isolateName[isolateId];
     final free = _isolateFreeSamples.last[index];
     final used = _isolateUsedSamples.last[index];
     final usedStr = Utils.formatSize(used);
     final capacity = free + used;
     final capacityStr = Utils.formatSize(capacity);
     return '${name} ($usedStr / $capacityStr)';
   }
 
-  Element _formatNativeOvercard(int row) => new DivElement()
+  static HtmlElement _formatNativeOvercard(int heap) => new DivElement()
     ..children = [
       new DivElement()
         ..classes = ['hovercard-title']
         ..text = 'Native',
       new DivElement()
         ..classes = ['hovercard-measure', 'hovercard-multi']
         ..children = [
           new DivElement()
             ..classes = ['hovercard-measure-label']
             ..text = 'Heap',
           new DivElement()
             ..classes = ['hovercard-measure-value']
-            ..text = Utils.formatSize(_vmSamples[row]),
+            ..text = Utils.formatSize(heap),
         ]
     ];
 
-  Element _formatIsolateOvercard(String isolateId, int row) {
-    final index = _isolateIndex[isolateId];
-    final free = _isolateFreeSamples[row][index];
-    final used = _isolateUsedSamples[row][index];
+  static HtmlElement _formatIsolateOvercard(String name, int free, int used) {
     final capacity = free + used;
     return new DivElement()
       ..children = [
         new DivElement()
           ..classes = ['hovercard-title']
-          ..text = _isolateName[isolateId],
+          ..text = name,
         new DivElement()
           ..classes = ['hovercard-measure', 'hovercard-multi']
           ..children = [
             new DivElement()
               ..classes = ['hovercard-measure-label']
               ..text = 'Heap Capacity',
             new DivElement()
               ..classes = ['hovercard-measure-value']
               ..text = Utils.formatSize(capacity),
           ],
@@ skipping 65 matching lines @@
   </defs>
 ''';
 
   StyleElement get style => new StyleElement()
     ..text = '''
 memory-graph svg .stacked-line-rdr-line:nth-child(2n+${_offset+1})
   path:nth-child(1) {
   filter: url(#stroke-grid);
 }''';
 }