VM: Refactor allocation stats code and remove duplicate code.

runtime/vm/scavenger.cc

 // Copyright (c) 2011, 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/scavenger.h"
 
 #include <algorithm>
 #include <map>
 #include <utility>
 
@@ skipping 853 matching lines @@
 }
 
 
 void Scavenger::WriteProtect(bool read_only) {
   ASSERT(!scavenging_);
   ASSERT(from_ == NULL);
   to_->WriteProtect(read_only);
 }
 
 
-void Scavenger::PrintToJSONObject(JSONObject* object) {
+void Scavenger::PrintToJSONObject(JSONObject* object) const {
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate != NULL);
   JSONObject space(object, "new");
   space.AddProperty("type", "HeapSpace");
   space.AddProperty("name", "new");
   space.AddProperty("vmName", "Scavenger");
   space.AddProperty("collections", collections());
   if (collections() > 0) {
     int64_t run_time = OS::GetCurrentTimeMicros() - isolate->start_time();
     run_time = Utils::Maximum(run_time, static_cast<int64_t>(0));
@@ skipping 18 matching lines @@
 }
 
 
 void Scavenger::FreeExternal(intptr_t size) {
   ASSERT(size >= 0);
   external_size_ -= size;
   ASSERT(external_size_ >= 0);
 }
 
 }  // namespace dart