Preventing our default handlers for ChromeOS to show up or confuse the user

chrome/browser/custom_handlers/protocol_handler_registry.h

 // Copyright (c) 2011 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_CUSTOM_HANDLERS_PROTOCOL_HANDLER_REGISTRY_H_
 #define CHROME_BROWSER_CUSTOM_HANDLERS_PROTOCOL_HANDLER_REGISTRY_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 173 matching lines @@
 
   // This is called by the UI thread when the system is shutting down. This
   // does finalization which must be done on the UI thread.
   void Finalize();
 
   // Registers the preferences that we store registered protocol handlers in.
   static void RegisterPrefs(PrefService* prefService);
 
   bool enabled() const { return enabled_; }
 
+  // Add a predefined protocol handler. This has to be called before the first
+  // load command was issued, otherwise the command will be ignored.
+  void AddFixedHandler(const ProtocolHandler& handler);
+
  private:
   friend class base::RefCountedThreadSafe<ProtocolHandlerRegistry>;
 
   // Puts the given handler at the top of the list of handlers for its
   // protocol.
   void PromoteHandler(const ProtocolHandler& handler);
 
   // Clears the default for the provided protocol.
   // Should be called only from the IO thread.
   void ClearDefaultIO(const std::string& scheme);
@@ skipping 66 matching lines @@
   // If false then registered protocol handlers will not be used to handle
   // requests.
   bool enabled_;
 
   // Copy of enabled_ that is only accessed on the IO thread.
   bool enabled_io_;
 
   // Whether or not we are loading.
   bool is_loading_;
 
+  // When the table gets loaded this flag will be set and any further calls to
+  // AddFixedHandler will be rejected.
+  bool is_loaded_;

[benwells, 2012/04/26 00:34:42]

Why is this necessary?

[Mr4D (OOO till 08-26), 2012/04/26 13:46:35]

It is a "debugging" helper: Default handlers can only be added before the load
call. After the load call they could overwrite user settings which isn't
allowed. As such a DCHECK will be used to check that this does not happen.

+
   DefaultClientObserverList default_client_observers_;
 
   // Copy of default_handlers_ that is only accessed on the IO thread.
   ProtocolHandlerMap default_handlers_io_;
 
   friend class ProtocolHandlerRegistryTest;
   friend class RegisterProtocolHandlerBrowserTest;
 
   DISALLOW_COPY_AND_ASSIGN(ProtocolHandlerRegistry);
 };
 #endif  // CHROME_BROWSER_CUSTOM_HANDLERS_PROTOCOL_HANDLER_REGISTRY_H_