Adds InitialRSS benchmark

runtime/vm/benchmark_test.cc

 // Copyright (c) 2012, 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/benchmark_test.h"
 
 #include "bin/builtin.h"
 #include "bin/file.h"
 #include "bin/isolate_data.h"
 
@@ skipping 712 matching lines @@
                                  buffer_len,
                                  thread);
     reader.ReadObject();
     free(buffer);
   }
   timer.Stop();
   int64_t elapsed_time = timer.TotalElapsedTime();
   benchmark->set_score(elapsed_time);
 }
 
+
+BENCHMARK_MEMORY(InitialRSS) {
+  benchmark->set_score(OS::MaxRSS());
+}
+
 }  // namespace dart