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

runtime/observatory/lib/src/service/object.dart

Index: runtime/observatory/lib/src/service/object.dart
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index e0f6e055920eee8fa6b9a594f19a7a0e95bfa2ca..7ce021770bdc1a5a9035c659de13577763f558fe 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -1521,12 +1521,13 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
     }
   }
 
-  Stream fetchHeapSnapshot(collectGarbage) {
+  Stream fetchHeapSnapshot(String roots, bool collectGarbage) {

[Cutch, 2016/11/18 20:40:31]

HeapSnapshotRoots roots

     if (_snapshotFetch == null || _snapshotFetch.isClosed) {
       _snapshotFetch = new StreamController.broadcast();
       // isolate.vm.streamListen('_Graph');
-      isolate.invokeRpcNoUpgrade(
-          '_requestHeapSnapshot', {'collectGarbage': collectGarbage});
+      isolate.invokeRpcNoUpgrade('_requestHeapSnapshot',
+                                 {'roots': roots,
+                                  'collectGarbage': collectGarbage});
     }
     return _snapshotFetch.stream;
   }