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

ppapi/native_client/src/trusted/plugin/service_runtime.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.
  */
 
 #define NACL_LOG_MODULE_NAME "Plugin::ServiceRuntime"
 
 #include "native_client/src/trusted/plugin/service_runtime.h"
 
@@ skipping 828 matching lines @@
 
 void ServiceRuntime::set_exit_status(int exit_status) {
   nacl::MutexLocker take(&mu_);
   exit_status_ = exit_status & 0xff;
 }
 
 nacl::string ServiceRuntime::GetCrashLogOutput() {
   if (NULL != subprocess_.get()) {
     return subprocess_->GetCrashLogOutput();
   } else {
-    return "";
+    return std::string();
   }
 }
 
 }  // namespace plugin