Review and cleanup lint warnings.

testing/utils/path_service.cpp

 // Copyright 2015 PDFium 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/utils/path_service.h"
 
 #ifdef _WIN32
 #include <Windows.h>
 #elif defined(__APPLE__)
 #include <mach-o/dyld.h>
 #else  // Linux
 #include <linux/limits.h>
 #include <unistd.h>
 #endif  // _WIN32
 
+#include <string>
+
 #include "core/include/fxcrt/fx_system.h"
 
 // static
 bool PathService::EndsWithSeparator(const std::string& path) {
   return path.size() > 1 && path[path.size() - 1] == PATH_SEPARATOR;
 }
 
 // static
 bool PathService::GetExecutableDir(std::string* path) {
 // Get the current executable file path.
@@ skipping 66 matching lines @@
 bool PathService::GetTestFilePath(const std::string& file_name,
                                   std::string* path) {
   if (!GetTestDataDir(path))
     return false;
 
   if (!EndsWithSeparator(*path))
     path->push_back(PATH_SEPARATOR);
   path->append(file_name);
   return true;
 }