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

runtime/observatory/lib/src/elements/class_view.dart

 // Copyright (c) 2013, 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.
 
 library class_view_element;
 
 import 'dart:async';
 import 'observatory_element.dart';
 import 'package:observatory/cpu_profile.dart';
 import 'package:observatory/elements.dart';
@@ skipping 17 matching lines @@
     return cls.evaluate(expression);
   }
 
   Future<ServiceObject> reachable(var limit) {
     return cls.isolate.getInstances(cls, limit).then((ServiceMap obj) {
       instances = obj;
     });
   }
 
   Future<ServiceObject> retainedToplist(var limit) {
-    return cls.isolate.fetchHeapSnapshot().last
+    return cls.isolate.fetchHeapSnapshot(true).last
       .then((HeapSnapshot snapshot) =>
           Future.wait(snapshot.getMostRetained(classId: cls.vmCid,
                                                limit: 10)))
       .then((List<ServiceObject> most) {
         mostRetained = new ObservableList.from(most);
       });
   }
 
   // TODO(koda): Add no-arg "calculate-link" instead of reusing "eval-link".
   Future<ServiceObject> reachableSize(var dummy) {
@@ skipping 63 matching lines @@
     return sampleBufferControlElement.reload(cls.isolate);
   }
 
   Future toggleAllocationTrace() {
     if (cls == null) {
       return new Future(refresh);
     }
     return cls.setTraceAllocations(!cls.traceAllocations).whenComplete(refresh);
   }
 }