[Sync] Make DirectoryBackingStore's db_ private.

sync/syncable/directory_backing_store_unittest.cc

 // Copyright 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 "testing/gtest/include/gtest/gtest.h"
 
 #include <string>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
@@ skipping 3144 matching lines @@
 TEST_F(DirectoryBackingStoreTest, MigrateVersion76To77) {
   sql::Connection connection;
   ASSERT_TRUE(connection.OpenInMemory());
   SetUpVersion76Database(&connection);
 
   scoped_ptr<TestDirectoryBackingStore> dbs(
       new TestDirectoryBackingStore(GetUsername(), &connection));
   ASSERT_FALSE(dbs->needs_column_refresh());
 
   EXPECT_EQ(GetExpectedLegacyMetaProtoTimes(INCLUDE_DELETED_ITEMS),
-            GetMetaProtoTimes(dbs->db_.get()));
+            GetMetaProtoTimes(&connection));
   // Since the proto times are expected to be in a legacy format, they may not
   // be compatible with ProtoTimeToTime, so we don't call ExpectTimes().
 
   ASSERT_TRUE(dbs->MigrateVersion76To77());
   ASSERT_EQ(77, dbs->GetVersion());
 
   EXPECT_EQ(GetExpectedMetaProtoTimes(INCLUDE_DELETED_ITEMS),
-            GetMetaProtoTimes(dbs->db_.get()));
+            GetMetaProtoTimes(&connection));
   // Cannot actually load entries due to version 77 not having all required
   // columns.
   ASSERT_FALSE(dbs->needs_column_refresh());
 }
 
 TEST_F(DirectoryBackingStoreTest, MigrateVersion77To78) {
   sql::Connection connection;
   ASSERT_TRUE(connection.OpenInMemory());
   SetUpVersion77Database(&connection);
 
@@ skipping 892 matching lines @@
 
   // At this point the handler has been posted but not executed.
   ASSERT_FALSE(was_called);
   // Pump the message loop and see that it is executed.
   base::RunLoop().RunUntilIdle();
   ASSERT_TRUE(was_called);
 }
 
 }  // namespace syncable
 }  // namespace syncer