Observatory improvements for exploring compiled code.

runtime/observatory/lib/src/elements/heap_snapshot.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 heap_snapshot_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:observatory/app.dart';
@@ skipping 47 matching lines @@
     firstColumn.style.justifyContent = 'flex-start';
     firstColumn.style.position = 'relative';
     firstColumn.style.alignItems = 'center';
     firstColumn.style.setProperty('overflow-x', 'hidden');
 
     var percentRetained = vertex.retainedSize / snapshot.graph.size;
     var percentNode = new SpanElement();
     percentNode.text =  Utils.formatPercentNormalized(percentRetained);
     percentNode.style.minWidth = '5em';
     percentNode.style.textAlign = 'right';
-    percentNode.title = "Retaining x of y.";
+    percentNode.title = "Percent of heap being retained";
     percentNode.style.display = 'inline-block';
     firstColumn.children.add(percentNode);
 
     var gap = new SpanElement();
     gap.style.minWidth = '1em';
     gap.style.display = 'inline-block';
     firstColumn.children.add(gap);
 
     AnyServiceRefElement objectRef = new Element.tag("any-service-ref");
     String hexAddress = vertex.address.toRadixString(16);
@@ skipping 373 matching lines @@
 
     new Future.delayed(const Duration(milliseconds: 500), () {
       buildMergedVertices(snapshot.graph).then((vertices) {
         state = 'Loaded';
         var rootRow = new MergedVerticesRow(tree, null, isolate, vertices);
         tree.initialize(rootRow);
       });
     });
   }
 }