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

runtime/vm/service.h

 // 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.
 
 #ifndef VM_SERVICE_H_
 #define VM_SERVICE_H_
 
 #include "include/dart_tools_api.h"
 
 #include "vm/allocation.h"
@@ skipping 87 matching lines @@
       void* user_data);
 
   static void SetEmbedderStreamCallbacks(
       Dart_ServiceStreamListenCallback listen_callback,
       Dart_ServiceStreamCancelCallback cancel_callback);
 
   static void SetGetServiceAssetsCallback(
       Dart_GetVMServiceAssetsArchive get_service_assets);
 
   static void SendEchoEvent(Isolate* isolate, const char* text);
-  static void SendGraphEvent(Thread* thread);
+  static void SendGraphEvent(Thread* thread, bool collect_garbage);
   static void SendInspectEvent(Isolate* isolate, const Object& inspectee);
 
   static void SendEmbedderEvent(Isolate* isolate,
                                 const char* stream_id,
                                 const char* event_kind,
                                 const uint8_t* bytes,
                                 intptr_t bytes_len);
 
   static void SendLogEvent(Isolate* isolate,
                            int64_t sequence_number,
@@ skipping 80 matching lines @@
   static bool needs_isolate_events_;
   static bool needs_debug_events_;
   static bool needs_gc_events_;
   static bool needs_echo_events_;
   static bool needs_graph_events_;
 };
 
 }  // namespace dart
 
 #endif  // VM_SERVICE_H_