HeapSnapshot: replace O(N*ln(N)) algorithm of sorting with O(N) one.

src/heap-snapshot-generator.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2675 matching lines @@
             writer_->AddCharacter('?');
           }
         }
     }
   }
   writer_->AddCharacter('\"');
 }
 
 
 void HeapSnapshotJSONSerializer::SerializeStrings() {
-  List<HashMap::Entry*> sorted_strings;
-  SortHashMap(&strings_, &sorted_strings);
+  ScopedVector<const unsigned char*> sorted_strings(
+      strings_.occupancy() + 1);
+  for (HashMap::Entry* entry = strings_.Start();
+      entry != NULL; entry = strings_.Next(entry)) {
+    sorted_strings[reinterpret_cast<uintptr_t>(entry->value)] =
+        reinterpret_cast<const unsigned char*>(entry->key);
+  }
   writer_->AddString("\"<dummy>\"");
-  for (int i = 0; i < sorted_strings.length(); ++i) {
+  for (int i = 1; i < sorted_strings.length(); ++i) {
     writer_->AddCharacter(',');
-    SerializeString(
-        reinterpret_cast<const unsigned char*>(sorted_strings[i]->key));
+    SerializeString(sorted_strings[i]);
     if (writer_->aborted()) return;
   }
 }
 
 
-template<typename T>
-inline static int SortUsingEntryValue(const T* x, const T* y) {
-  uintptr_t x_uint = reinterpret_cast<uintptr_t>((*x)->value);
-  uintptr_t y_uint = reinterpret_cast<uintptr_t>((*y)->value);
-  if (x_uint > y_uint) {
-    return 1;
-  } else if (x_uint == y_uint) {
-    return 0;
-  } else {
-    return -1;
-  }
-}
-
-
-void HeapSnapshotJSONSerializer::SortHashMap(
-    HashMap* map, List<HashMap::Entry*>* sorted_entries) {
-  for (HashMap::Entry* p = map->Start(); p != NULL; p = map->Next(p))
-    sorted_entries->Add(p);
-  sorted_entries->Sort(SortUsingEntryValue);
-}
-
 } }  // namespace v8::internal