Rewrite std::string("") to std::string(), Linux edition.

sync/notifier/sync_system_resources_unittest.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/notifier/sync_system_resources.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 150 matching lines @@
 TEST_F(SyncSystemResourcesTest, WriteState) {
   sync_system_resources_.Start();
   EXPECT_CALL(mock_state_writer_, WriteState(_));
   // Owned by WriteState.
   MockStorageCallback mock_storage_callback;
   invalidation::Status results(invalidation::Status::PERMANENT_FAILURE,
                                "fake-failure");
   EXPECT_CALL(mock_storage_callback, Run(_))
       .WillOnce(SaveArg<0>(&results));
   sync_system_resources_.storage()->WriteKey(
-      "", "state", mock_storage_callback.CreateCallback());
+      std::string(), "state", mock_storage_callback.CreateCallback());
   message_loop_.RunUntilIdle();
-  EXPECT_EQ(invalidation::Status(invalidation::Status::SUCCESS, ""), results);
+  EXPECT_EQ(invalidation::Status(invalidation::Status::SUCCESS, std::string()),
+            results);
 }
 
 }  // namespace
 }  // namespace syncer