[SyncFS] Support Delete operation on LevelDBWrapper::Iterator

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.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 "chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.h"
 
 #include <map>
 #include <set>
 #include <string>
 
@@ skipping 49 matching lines @@
       db_iterator_->Next();
     if (comp >= 0)
       ++map_iterator_;
   } else {
     ++map_iterator_;
   }
 
   AdvanceIterators();
 }
 
+void LevelDBWrapper::Iterator::Delete() {
+  DCHECK(Valid());
+
+  const std::string key_str = key().ToString();
+  Transaction deletion(DELETE_OPERATION, std::string());
+  std::pair<PendingOperationMap::iterator, bool> inserted =
+      db_->pending_.insert(std::make_pair(key_str, deletion));

[tzik, 2014/08/12 06:28:33]

Can we put previous iterator as a hint like this?
insert(map_iterator_, std::make_pair(...))

[peria, 2014/08/12 06:41:48]

We can, but if we can add a hint, insert() returns an iterator, not a pair.
We need a pair to detect the element is newly added or not,
so we cannot use the hint.
http://www.cplusplus.com/reference/map/map/insert/

[tzik, 2014/08/12 07:32:36]

Ah, I wasn't aware that.
How about doing like below?
map_iterator_ = insert(map_iterator, std::make_pair(...));
map_iterator_->second = Transaction();

[peria, 2014/08/12 07:44:35]

Done.

+  map_iterator_ = inserted.first;
+  if (!inserted.second)
+    map_iterator_->second = deletion;
+
+  AdvanceIterators();
+}
+
 leveldb::Slice LevelDBWrapper::Iterator::key() {
   DCHECK(Valid());
 
   if (!db_iterator_->Valid())
     return map_iterator_->first;
   if (map_iterator_ == db_->pending_.end())
     return db_iterator_->key();
 
   const leveldb::Slice db_key = db_iterator_->key();
   const leveldb::Slice map_key = map_iterator_->first;
@@ skipping 112 matching lines @@
 void LevelDBWrapper::Clear() {
   pending_.clear();
 }
 
 leveldb::DB* LevelDBWrapper::GetLevelDB() {
   return db_.get();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system