Add a version of heap snapshots that use only fields and stack frames as roots and only include ins…

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

 // Copyright (c) 2016, 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.
 
 part of heap_snapshot;
 
 class HeapSnapshot implements M.HeapSnapshot {
   ObjectGraph graph;
   DateTime timestamp;
   int get objects => graph.vertexCount;
@@ skipping 106 matching lines @@
     }
     return result;
   }
 }
 
 class HeapSnapshotDominatorNode implements M.HeapSnapshotDominatorNode {
   final ObjectVertex v;
   final S.Isolate isolate;
   S.HeapObject _preloaded;
 
+  bool get isStack => v.isStack;
+
   Future<S.HeapObject> get object {
     if (_preloaded != null) {
       return new Future.value(_preloaded);
     } else {
       return isolate.getObjectByAddress(v.address).then((S.HeapObject obj) {
         return _preloaded = obj;
       });
     }
   }
 
@@ skipping 15 matching lines @@
   HeapSnapshotDominatorNode(S.Isolate isolate, ObjectVertex vertex)
       : isolate = isolate,
         v = vertex;
 }
 
 class HeapSnapshotMergedDominatorNode
     implements M.HeapSnapshotMergedDominatorNode {
   final MergedObjectVertex v;
   final S.Isolate isolate;
 
+  bool get isStack => v.isStack;
+
   Future<S.HeapObject> get klass {
     return new Future.value(isolate.getClassByCid(v.vmCid));
   }
 
   Iterable<HeapSnapshotMergedDominatorNode> _children;
   Iterable<HeapSnapshotMergedDominatorNode> get children {
     if (_children != null) {
       return _children;
     } else {
       return _children =
@@ skipping 82 matching lines @@
   final MergedEdge edge;
   S.Class get target => edge.sourceVertex != vertex
       ? edge.sourceVertex.clazz
       : edge.targetVertex.clazz;
   int get count => edge.count;
   int get shallowSize => edge.shallowSize;
   int get retainedSize => edge.retainedSize;
 
   HeapSnapshotClassOutbound(this.vertex, this.edge);
 }