leveldb_service: Attempt to fix deadlock on shutdown.

components/leveldb/leveldb_database_impl.cc

 // Copyright 2016 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/leveldb_database_impl.h"
 
+#include <map>
+#include <string>
+
 #include "base/rand_util.h"
 #include "components/leveldb/env_mojo.h"
 #include "components/leveldb/util.h"
 #include "mojo/common/common_type_converters.h"
 #include "third_party/leveldatabase/src/include/leveldb/db.h"
 #include "third_party/leveldatabase/src/include/leveldb/write_batch.h"
 
 namespace leveldb {
 namespace {
 
@@ skipping 83 matching lines @@
     db_->ReleaseSnapshot(it->second);
     snapshot_map_.erase(it);
   }
 }
 
 void LevelDBDatabaseImpl::GetFromSnapshot(uint64_t snapshot_id,
                                           mojo::Array<uint8_t> key,
                                           const GetCallback& callback) {
   // If the snapshot id is invalid, send back invalid argument
   auto it = snapshot_map_.find(snapshot_id);
-  if (it == snapshot_map_.end())
+  if (it == snapshot_map_.end()) {
     callback.Run(DatabaseError::INVALID_ARGUMENT, mojo::Array<uint8_t>());
+    return;
+  }
 
   std::string value;
   leveldb::ReadOptions options;
   options.snapshot = it->second;
   leveldb::Status status = db_->Get(options, GetSliceFor(key), &value);
   callback.Run(LeveldbStatusToError(status), mojo::Array<uint8_t>::From(value));
 }
 
 }  // namespace leveldb