All together now

content/public/common/desktop_media_id.h

 // Copyright 2013 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 CONTENT_PUBLIC_COMMON_DESKTOP_MEDIA_ID_H_
 #define CONTENT_PUBLIC_COMMON_DESKTOP_MEDIA_ID_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 28 matching lines @@
   // Operators so that DesktopMediaID can be used with STL containers.
   bool operator<(const DesktopMediaID& other) const {
     return type < other.type || (type == other.type && id < other.id);
   }
   bool operator==(const DesktopMediaID& other) const {
     return type == other.type && id == other.id;
   }
 
   bool is_null() { return type == TYPE_NONE; }
 
-  std::string ToString();
+  std::string ToString() const;
 
   Type type;
   Id id;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_DESKTOP_MEDIA_ID_H_