Expose in memory Env to the world

Summary: That will help with some iOS testing I'm doing.

Test Plan: compiles

Reviewers: dhruba, haobo, ljin, yhchiang, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17787

Author: igorcanadi

helpers/memenv/memenv.cc

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#include "helpers/memenv/memenv.h"
-
 #include "rocksdb/env.h"
 #include "rocksdb/status.h"
 #include "port/port.h"

helpers/memenv/memenv.h

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#include "helpers/memenv/memenv.h"
-
 #include "db/db_impl.h"
 #include "rocksdb/db.h"
 #include "rocksdb/env.h"

helpers/memenv/memenv_test.cc

@@ -761,6 +761,12 @@ class EnvWrapper : public Env {
   Env* target_;
 };
 
+// Returns a new environment that stores its data in memory and delegates
+// all non-file-storage tasks to base_env. The caller must delete the result
+// when it is no longer needed.
+// *base_env must remain live while the result is in use.
+Env* NewMemEnv(Env* base_env);
+
 }  // namespace rocksdb
 
 #endif  // STORAGE_ROCKSDB_INCLUDE_ENV_H_