Perform a full GC by default when requesting a heap snapshot.

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

 // Copyright (c) 2014, 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 service;
 
 // Some value smaller than the object ring, so requesting a large array
 // doesn't result in an expired ref because the elements lapped it in the
 // object ring.
 const int kDefaultFieldLimit = 100;
@@ skipping 1347 matching lines @@
 
     latestSnapshot = new HeapSnapshot(this, loadedChunks, event.nodeCount);
     if (_snapshotFetch != null) {
       latestSnapshot.graph.process(_snapshotFetch).then((graph) {
         _snapshotFetch.add(latestSnapshot);
         _snapshotFetch.close();
       });
     }
   }
 
-  Stream fetchHeapSnapshot() {
+  Stream fetchHeapSnapshot(collectGarbage) {
     if (_snapshotFetch == null || _snapshotFetch.isClosed) {
       _snapshotFetch = new StreamController();
       // isolate.vm.streamListen('_Graph');
-      isolate.invokeRpcNoUpgrade('_requestHeapSnapshot', {});
+      isolate.invokeRpcNoUpgrade('_requestHeapSnapshot',
+                                 {'collectGarbage': collectGarbage});
     }
     return _snapshotFetch.stream;
   }
 
   void updateHeapsFromMap(ObservableMap map) {
     newSpace.update(map['new']);
     oldSpace.update(map['old']);
   }
 
   void _update(ObservableMap map, bool mapIsRef) {
@@ skipping 2637 matching lines @@
     var v = list[i];
     if ((v is ObservableMap) && _isServiceMap(v)) {
       list[i] = owner.getFromMap(v);
     } else if (v is ObservableList) {
       _upgradeObservableList(v, owner);
     } else if (v is ObservableMap) {
       _upgradeObservableMap(v, owner);
     }
   }
 }