[vm-service] Use consistent success response for _requestHeapSnapshot.

runtime/vm/service.cc

 // 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.
 
 #include "vm/service.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/globals.h"
 
@@ skipping 3492 matching lines @@
   const char* roots_arg = js->LookupParam("roots");
   if (roots_arg != NULL) {
     roots = EnumMapper(roots_arg, snapshot_roots_names, snapshot_roots_values);
   }
   const bool collect_garbage =
       BoolParameter::Parse(js->LookupParam("collectGarbage"), true);
   if (Service::graph_stream.enabled()) {
     Service::SendGraphEvent(thread, roots, collect_garbage);
   }
   // TODO(koda): Provide some id that ties this request to async response(s).
-  JSONObject jsobj(js);
-  jsobj.AddProperty("type", "OK");
+  PrintSuccess(js);
   return true;
 }
 
 
 void Service::SendGraphEvent(Thread* thread,
                              ObjectGraph::SnapshotRoots roots,
                              bool collect_garbage) {
   uint8_t* buffer = NULL;
   WriteStream stream(&buffer, &allocator, 1 * MB);
   ObjectGraph graph(thread);
@@ skipping 806 matching lines @@
     if (strcmp(method_name, method.name) == 0) {
       return &method;
     }
   }
   return NULL;
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart