components: Cleanup class/struct fwd declarations

components/leveldb/leveldb_database_impl.h

 // 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.
 
 #ifndef COMPONENTS_LEVELDB_LEVELDB_DATABASE_IMPL_H_
 #define COMPONENTS_LEVELDB_LEVELDB_DATABASE_IMPL_H_
 
 #include <memory>
 
 #include "base/unguessable_token.h"
 #include "components/leveldb/public/interfaces/leveldb.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "third_party/leveldatabase/src/include/leveldb/db.h"
 
 namespace leveldb {
 
-class MojoEnv;
-
 // The backing to a database object that we pass to our called.
 class LevelDBDatabaseImpl : public mojom::LevelDBDatabase {
  public:
   LevelDBDatabaseImpl(std::unique_ptr<leveldb::Env> environment,
                       std::unique_ptr<leveldb::DB> db);
   ~LevelDBDatabaseImpl() override;
 
   // Overridden from LevelDBDatabase:
   void Put(const std::vector<uint8_t>& key,
            const std::vector<uint8_t>& value,
@@ skipping 52 matching lines @@
   // system, but this maybe should be fixed...
 
   std::map<base::UnguessableToken, Iterator*> iterator_map_;
 
   DISALLOW_COPY_AND_ASSIGN(LevelDBDatabaseImpl);
 };
 
 }  // namespace leveldb
 
 #endif  // COMPONENTS_LEVELDB_LEVELDB_DATABASE_IMPL_H_