[SyncFS] Support Delete operation on LevelDBWrapper::Iterator

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc

Index: chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc b/chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc
index 3200b302366b4691d26c7741a93fb6deea69d4be..b4c1e5ba6504ddbafc494a349f9cda11c5ddacab 100644
--- a/chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc
+++ b/chrome/browser/sync_file_system/drive_backend/leveldb_wrapper.cc
@@ -67,6 +67,14 @@ void LevelDBWrapper::Iterator::Next() {
   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());