Cleanup: Pass std::string as const reference if possible

chrome/browser/chromeos/drive/file_system_util.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_UTIL_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_UTIL_H_
 
 #include <string>
 
 #include "base/callback_forward.h"
@@ skipping 13 matching lines @@
 class DriveServiceInterface;
 class FileSystemInterface;
 
 namespace util {
 
 // Returns the Drive mount point path, which looks like "/special/drive-<hash>".
 base::FilePath GetDriveMountPointPath(Profile* profile);
 
 // Returns the Drive mount point path, which looks like
 // "/special/drive-<username_hash>", when provided with the |user_id_hash|.
-base::FilePath GetDriveMountPointPathForUserIdHash(std::string user_id_hash);
+base::FilePath GetDriveMountPointPathForUserIdHash(
+    const std::string& user_id_hash);
 
 // Returns true if the given path is under the Drive mount point.
 bool IsUnderDriveMountPoint(const base::FilePath& path);
 
 // Extracts the Drive path from the given path located under the Drive mount
 // point. Returns an empty path if |path| is not under the Drive mount point.
 // Examples: ExtractDrivePath("/special/drive-xxx/foo.txt") => "drive/foo.txt"
 base::FilePath ExtractDrivePath(const base::FilePath& path);
 
 // Returns the FileSystem for the |profile|. If not available (not mounted
@@ skipping 78 matching lines @@
   DRIVE_CONNECTED,
 };
 
 // Returns the Drive connection status for the |profile|.
 ConnectionStatusType GetDriveConnectionStatus(Profile* profile);
 
 }  // namespace util
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_UTIL_H_