[Sync] Make DirectoryBackingStore's db_ private.

sync/syncable/in_memory_directory_backing_store.cc

 // Copyright (c) 2012 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 "sync/syncable/in_memory_directory_backing_store.h"
 
 namespace syncer {
 namespace syncable {
 
 InMemoryDirectoryBackingStore::InMemoryDirectoryBackingStore(
     const std::string& dir_name)
     : DirectoryBackingStore(dir_name),
       consistent_cache_guid_requested_(false) {
 }
 
 DirOpenResult InMemoryDirectoryBackingStore::Load(
     Directory::MetahandlesMap* handles_map,
     JournalIndex* delete_journals,
     MetahandleSet* metahandles_to_purge,
     Directory::KernelLoadInfo* kernel_load_info) {
-  if (!db_->is_open()) {
-    if (!db_->OpenInMemory())
+  if (!IsOpen()) {
+    if (!OpenInMemory())
       return FAILED_OPEN_DATABASE;
   }
 
   if (!InitializeTables())
     return FAILED_OPEN_DATABASE;
 
   if (consistent_cache_guid_requested_) {
-    if (!db_->Execute("UPDATE share_info "
-                      "SET cache_guid = 'IrcjZ2jyzHDV9Io4+zKcXQ=='")) {
+    if (!db()->Execute(
+            "UPDATE share_info "
+            "SET cache_guid = 'IrcjZ2jyzHDV9Io4+zKcXQ=='")) {
       return FAILED_OPEN_DATABASE;
     }
   }
 
   if (!LoadEntries(handles_map, metahandles_to_purge))
     return FAILED_DATABASE_CORRUPT;
   if (!LoadDeleteJournals(delete_journals))
     return FAILED_DATABASE_CORRUPT;
   if (!LoadInfo(kernel_load_info))
     return FAILED_DATABASE_CORRUPT;
   if (!VerifyReferenceIntegrity(handles_map))
     return FAILED_DATABASE_CORRUPT;
 
   return OPENED;
 }
 
 }  // namespace syncable
 }  // namespace syncer