Media Keys should not count towards the max of four shortcuts per extension.

chrome/common/extensions/command.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_COMMON_EXTENSIONS_COMMAND_H_
 #define CHROME_COMMON_EXTENSIONS_COMMAND_H_
 
 #include <map>
 #include <string>
 
@@ skipping 24 matching lines @@
 
   // Parse a string as an accelerator. If the accelerator is unparsable then
   // a generic ui::Accelerator object will be returns (with key_code Unknown).
   static ui::Accelerator StringToAccelerator(const std::string& accelerator,
                                              const std::string& command_name);
 
   // Returns the string representation of an accelerator without localizing the
   // shortcut text (like accelerator::GetShortcutText() does).
   static std::string AcceleratorToString(const ui::Accelerator& accelerator);
 
+  // Return true if the specified accelerator is one of the following multimedia
+  // keys: Next Track key, Previous Track key, Stop Media key, Play/Pause Media
+  // key, without any modifiers.
+  static bool IsMediaKey(const ui::Accelerator& accelerator);
+
   // Parse the command.
   bool Parse(const base::DictionaryValue* command,
              const std::string& command_name,
              int index,
              base::string16* error);
 
   // Convert a Command object from |extension| to a DictionaryValue.
   // |active| specifies whether the command is active or not.
   base::DictionaryValue* ToValue(
       const Extension* extension, bool active) const;
@@ skipping 18 matching lines @@
   base::string16 description_;
   bool global_;
 };
 
 // A mapping of command name (std::string) to a command object.
 typedef std::map<std::string, Command> CommandMap;
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_COMMAND_H_