First part to fix Bug 50726 "Save extension list and "winning" prefs from extensions"

chrome/browser/extensions/extension_prefs.h

 // Copyright (c) 2010 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_EXTENSIONS_EXTENSION_PREFS_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_
 #pragma once
 
 #include <set>
 #include <string>
@@ skipping 174 matching lines @@
 
   // Gets the next available application launch index. This is 1 higher than the
   // highest current application launch index found.
   int GetNextAppLaunchIndex();
 
   static void RegisterUserPrefs(PrefService* prefs);
 
   // The underlying PrefService.
   PrefService* pref_service() const { return prefs_; }
 
+  // Persists the vector of extension ids |precedence|.
+  // See ExtensionPrefs::GetExtensionPrecedences for its semantics.
+  //
+  // Note: This function only persists the vector in the PrefStore. Precedences
+  // are actually managed by ExtensionPrefStore. Therefore, only that class
+  // should call PersistExtensionPrecedences.
+  void PersistExtensionPrecedences(const std::vector<std::string>& precedence);
+
+  // Fills the |precedence| vector with the extension ids in increasing
+  // order of precedence. Higher precedence means that an extension may
+  // overwrite settings of an extension with lower precedence.
+  // As of now, the precedence is determined by installation order and
+  // updated by OnExtensionInstalled and OnExtensionUninstalled.
+  void GetExtensionPrecedences(std::vector<std::string>* precedence) const;
+
  private:
   // Converts absolute paths in the pref to paths relative to the
   // install_directory_.
   void MakePathsRelative();
 
   // Converts internal relative paths to be absolute. Used for export to
   // consumers who expect full paths.
   void MakePathsAbsolute(DictionaryValue* dict);
 
   // Sets the pref |key| for extension |id| to |value|.
@@ skipping 51 matching lines @@
   // Base extensions install directory.
   FilePath install_directory_;
 
   // The URLs of all of the toolstrips.
   URLList shelf_order_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionPrefs);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_PREFS_H_