[Sync] Fixing easy lint violations.

components/sync/core/model_type_store_backend.h

 // Copyright 2015 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_SYNC_CORE_MODEL_TYPE_STORE_BACKEND_H_
 #define COMPONENTS_SYNC_CORE_MODEL_TYPE_STORE_BACKEND_H_
 
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ skipping 49 matching lines @@
       ModelTypeStore::RecordList* record_list);
 
   // Writes modifications accumulated in |write_batch| to database.
   ModelTypeStore::Result WriteModifications(
       std::unique_ptr<leveldb::WriteBatch> write_batch);
 
  private:
   friend class base::RefCountedThreadSafe<ModelTypeStoreBackend>;
   friend class ModelTypeStoreBackendTest;
 
-  ModelTypeStoreBackend(const std::string& path);
+  explicit ModelTypeStoreBackend(const std::string& path);
   ~ModelTypeStoreBackend();
 
   // In some scenarios ModelTypeStoreBackend holds ownership of env. Typical
   // example is when test creates in memory environment with CreateInMemoryEnv
   // and wants it to be destroyed along with backend. This is achieved by
   // passing ownership of env to TakeEnvOwnership function.
   //
   // env_ declaration should appear before declaration of db_ because
   // environment object should still be valid when db_'s destructor is called.
   std::unique_ptr<leveldb::Env> env_;
@@ skipping 18 matching lines @@
 
   // Macro wrapped mutex to guard against concurrent calls in debug builds.
   DFAKE_MUTEX(push_pop_);
 
   DISALLOW_COPY_AND_ASSIGN(ModelTypeStoreBackend);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_CORE_MODEL_TYPE_STORE_BACKEND_H_