Pacify Coverity when reading kExtensionsPref dictionary

chrome/browser/prefs/pref_service.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.
 
 // This provides a way to access the application's current preferences.
 
 #ifndef CHROME_BROWSER_PREFS_PREF_SERVICE_H_
 #define CHROME_BROWSER_PREFS_PREF_SERVICE_H_
 #pragma once
 
@@ skipping 149 matching lines @@
 
   // If the path is valid and the value at the end of the path matches the type
   // specified, it will return the specified value.  Otherwise, the default
   // value (set when the pref was registered) will be returned.
   bool GetBoolean(const char* path) const;
   int GetInteger(const char* path) const;
   double GetReal(const char* path) const;
   std::string GetString(const char* path) const;
   FilePath GetFilePath(const char* path) const;
 
-  // Returns the branch if it exists.  If it's not a branch or the branch does
-  // not exist, returns NULL.
+  // Returns the branch if it exists, or the registered default value otherwise.
+  // Note that |path| must point to a registered preference. In that case, these
+  // functions will never return NULL.
   const DictionaryValue* GetDictionary(const char* path) const;
   const ListValue* GetList(const char* path) const;
 
   // Removes a user pref and restores the pref to its default value.
   void ClearPref(const char* path);
 
   // If the path is valid (i.e., registered), update the pref value in the user
   // prefs. Seting a null value on a preference of List or Dictionary type is
   // equivalent to removing the user value for that preference, allowing the
   // default value to take effect unless another value takes precedence.
@@ skipping 85 matching lines @@
   PrefService(const PrefService& original,
               PrefStore* incognito_extension_prefs);
 
   // If the pref at the given path changes, we call the observer's Observe
   // method with PREF_CHANGED. Note that observers should not call these methods
   // directly but rather use a PrefChangeRegistrar to make sure the observer
   // gets cleaned up properly.
   virtual void AddPrefObserver(const char* path, NotificationObserver* obs);
   virtual void RemovePrefObserver(const char* path, NotificationObserver* obs);
 
-  // Add a preference to the PreferenceMap.  If the pref already exists, return
-  // false.  This method takes ownership of |default_value|.
+  // Registers a new preference at |path|. The |default_value| must not be
+  // NULL as it determines the preference value's type.
+  // RegisterPreference must not be called twice for the same path.
+  // This method takes ownership of |default_value|.
   void RegisterPreference(const char* path, Value* default_value);
 
   // Sets the value for this pref path in the user pref store and informs the
   // PrefNotifier of the change.
   void SetUserPrefValue(const char* path, Value* new_value);
 
   // Load preferences from storage, attempting to diagnose and handle errors.
   // This should only be called from the constructor.
   void InitFromStorage();
 
   // The PrefValueStore provides prioritized preference values. It is created
   // and owned by this PrefService. Subclasses may access it for unit testing.
   scoped_ptr<PrefValueStore> pref_value_store_;
 
   // Pref Stores and profile that we passed to the PrefValueStore.
   scoped_refptr<PersistentPrefStore> user_pref_store_;
   scoped_refptr<DefaultPrefStore> default_store_;
 
   // Local cache of registered Preference objects. The default_store_
   // is authoritative with respect to what the types and default values
   // of registered preferences are.
   mutable PreferenceSet prefs_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefService);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_SERVICE_H_