Extended the ProtoDatabase to provide LoadKeys() functionality.

components/leveldb_proto/leveldb_database.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/leveldb_proto/leveldb_database.h"
 
 #include <string>
 #include <vector>
 
 #include "base/files/file_path.h"
@@ skipping 105 matching lines @@
   leveldb::ReadOptions options;
   std::unique_ptr<leveldb::Iterator> db_iterator(db_->NewIterator(options));
   for (db_iterator->SeekToFirst(); db_iterator->Valid(); db_iterator->Next()) {
     leveldb::Slice value_slice = db_iterator->value();
     std::string entry(value_slice.data(), value_slice.size());
     entries->push_back(entry);
   }
   return true;
 }
 
+bool LevelDB::LoadKeys(std::vector<std::string>* keys) {
+  DFAKE_SCOPED_LOCK(thread_checker_);
+  if (!db_)
+    return false;
+
+  leveldb::ReadOptions options;
+  options.fill_cache = false;
+  std::unique_ptr<leveldb::Iterator> db_iterator(db_->NewIterator(options));
+  for (db_iterator->SeekToFirst(); db_iterator->Valid(); db_iterator->Next()) {
+    leveldb::Slice key_slice = db_iterator->key();
+    keys->push_back(std::string(key_slice.data(), key_slice.size()));
+  }
+  return true;
+}
+
 bool LevelDB::Get(const std::string& key, bool* found, std::string* entry) {
   DFAKE_SCOPED_LOCK(thread_checker_);
   if (!db_)
     return false;
 
   leveldb::ReadOptions options;
   leveldb::Status status = db_->Get(options, key, entry);
   if (status.ok()) {
     *found = true;
     return true;
   }
   if (status.IsNotFound()) {
     *found = false;
     return true;
   }
 
   DLOG(WARNING) << "Failed loading leveldb_proto entry with key \"" << key
                 << "\": " << status.ToString();
   return false;
 }
 
 }  // namespace leveldb_proto