[observatory] Add an "ownership" analysis for the heap snapshot.

runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart

Index: runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
diff --git a/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart b/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
index 37c6bf56410f98611dc21caf071fdfd21e1ac6df..7e56fd9366f9c506ac7378015ac4530e417dca5d 100644
--- a/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
+++ b/runtime/observatory/lib/src/heap_snapshot/heap_snapshot.dart
@@ -13,6 +13,7 @@ class HeapSnapshot implements M.HeapSnapshot {
   HeapSnapshotDominatorNode dominatorTree;
   HeapSnapshotMergedDominatorNode mergedDominatorTree;
   List<MergedVertex> classReferences;
+  List<HeapSnapshotOwnershipClass> ownershipClasses;
 
   static Future sleep([Duration duration = const Duration(microseconds: 0)]) {
     final Completer completer = new Completer();
@@ -40,6 +41,7 @@ class HeapSnapshot implements M.HeapSnapshot {
       mergedDominatorTree =
           new HeapSnapshotMergedDominatorNode(isolate, graph.mergedRoot);
       classReferences = await buildMergedVertices(isolate, graph, signal);
+      ownershipClasses = buildOwnershipClasses(isolate, graph);
       progress.close();
     }());
     return progress.stream;
@@ -100,6 +102,18 @@ class HeapSnapshot implements M.HeapSnapshot {
     return cidToMergedVertex.values.toList();
   }
 
+  buildOwnershipClasses(S.Isolate isolate, ObjectGraph graph) {
+    var numCids = graph.numCids;
+    var classes = new List();
+    for (var cid = 0; cid < numCids; cid++) {
+      var size = graph.getOwnedByCid(cid);
+      if (size != 0) {
+        classes.add(new HeapSnapshotOwnershipClass(cid, isolate, size));
+      }
+    }
+    return classes;
+  }
+
   List<Future<S.ServiceObject>> getMostRetained(S.Isolate isolate,
       {int classId, int limit}) {
     var result = [];
@@ -267,3 +281,12 @@ class HeapSnapshotClassOutbound implements M.HeapSnapshotClassOutbound {
 
   HeapSnapshotClassOutbound(this.vertex, this.edge);
 }
+
+class HeapSnapshotOwnershipClass implements M.HeapSnapshotOwnershipClass {
+  final int cid;
+  final S.Isolate isolate;
+  S.Class get clazz => isolate.getClassByCid(cid);
+  final int size;
+
+  HeapSnapshotOwnershipClass(this.cid, this.isolate, this.size);
+}