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

chrome/browser/extensions/extension_prefs.h

Index: chrome/browser/extensions/extension_prefs.h
diff --git a/chrome/browser/extensions/extension_prefs.h b/chrome/browser/extensions/extension_prefs.h
index eb16329357df7b3e80c46faf29897968ef076442..94bc600c00a0e849ff4b59e49eaeefc262b68507 100644
--- a/chrome/browser/extensions/extension_prefs.h
+++ b/chrome/browser/extensions/extension_prefs.h
@@ -192,6 +192,21 @@ class ExtensionPrefs {
   // 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_.