[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();
+  db_->Delete(key_str);
+  Seek(key_str);

[tzik, 2014/08/12 03:37:32]

Can this be like below?
  map_iterator->second = Transaction(DELETE_OPERATION, std::string());
  AdvanceIterators();

[peria, 2014/08/12 05:46:36]

As we chatted offline, it does not work if |db_->pending_| does not
have an element with the key.

I (remove and) insert the element, instead.  How is it?

+}
+
 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