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

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

Index: runtime/observatory/lib/src/models/objects/heap_snapshot.dart
diff --git a/runtime/observatory/lib/src/models/objects/heap_snapshot.dart b/runtime/observatory/lib/src/models/objects/heap_snapshot.dart
index ff4cefeccd9636a7fe9a63769f8408b9a4c299c3..aae5493e853f0ef29376eb8ea5a246df4e8c1d46 100644
--- a/runtime/observatory/lib/src/models/objects/heap_snapshot.dart
+++ b/runtime/observatory/lib/src/models/objects/heap_snapshot.dart
@@ -4,6 +4,8 @@
 
 part of models;
 
+enum HeapSnapshotRoots { user, vm }
+
 abstract class HeapSnapshot {
   DateTime get timestamp;
   int get objects;
@@ -17,6 +19,7 @@ abstract class HeapSnapshot {
 abstract class HeapSnapshotDominatorNode {
   int get shallowSize;
   int get retainedSize;
+  bool get isStack;
   Future<ObjectRef> get object;
   Iterable<HeapSnapshotDominatorNode> get children;
 }
@@ -25,6 +28,7 @@ abstract class HeapSnapshotMergedDominatorNode {
   int get instanceCount;
   int get shallowSize;
   int get retainedSize;
+  bool get isStack;
   Future<ObjectRef> get klass;
   Iterable<HeapSnapshotMergedDominatorNode> get children;
 }