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

chrome/browser/extensions/extension_pref_store.h

Index: chrome/browser/extensions/extension_pref_store.h
diff --git a/chrome/browser/extensions/extension_pref_store.h b/chrome/browser/extensions/extension_pref_store.h
index f1767589a9aee4a67b2dec4814c4e19716e3803f..67c7335c05af5922c705254dd628bee72e0011e5 100644
--- a/chrome/browser/extensions/extension_pref_store.h
+++ b/chrome/browser/extensions/extension_pref_store.h
@@ -30,6 +30,15 @@ class Value;
 // proxy settings. A stack of relevant extensions is stored in order of
 // their addition to this PrefStore. For each preference, the last-added
 // enabled extension that tries to set it overrules any others.
+//
+// TODO(battre): The ExtensionPrefStore has an issue if it serves for storing
+// extension preferences in the local-state (shared among all profiles on a
+// machine). In this context, there is no meaningful definition of a precedence
+// order as the same extensions can be installed in different profiles.
+// One instance would override the preferences of another instance. Also it is
+// unclear how settings should be removed in this case. For this reason we
+// (pamg, battre) decided to not support the ExtensionPrefStore for local-state.
+// This needs to be enforced by the code.
 class ExtensionPrefStore : public PrefStore,
                            public NotificationObserver {
  public:
@@ -72,13 +81,21 @@ class ExtensionPrefStore : public PrefStore,
   // subclasses for unit-testing.
   virtual PrefService* GetPrefService();
 
+  // The following functions delegate to
+  // profile_->GetExtensionsService()->extension_prefs()
+  // and are defined here only for injection in case of unit tests.
+  virtual void PersistExtensionPrecedences(
+      const std::vector<std::string>& precedence);
+  virtual void GetExtensionPrecedences(
+      std::vector<std::string>* precedence) const;
+
  private:
   // Associates an extension with the prefs it sets. Owns the pref values.
   struct ExtensionPrefs {
-    ExtensionPrefs(const Extension* extension, PrefValueMap* values);
+    ExtensionPrefs(const std::string& extension_id, PrefValueMap* values);
     ~ExtensionPrefs();
 
-    const Extension* extension;
+    std::string extension_id;
     PrefValueMap* pref_values;
   };
 
@@ -102,6 +119,23 @@ class ExtensionPrefStore : public PrefStore,
                const NotificationSource& source,
                const NotificationDetails& details);
 
+  // The following functions update the precedence list maintained by
+  // ExtensionPrefs. They are not responsible for updating the |prefs_| cache.
+  // Therefore, they should not be called outside of InstallExtensionPref and
+  // UninstallExtension.
+
+  // Appends |extension_id| to the end of the precedence list. This makes
+  // |extension_id| the extension that overwrites preferences of all other
+  // extensions.
+  void AddPrecedence(const std::string& extension_id);
+
+  // Removes |extension_id| from the precedence list.
+  void RemovePrecedence(const std::string& extension_id);
+
+  // Initializes the extension_stack_ with empty dictionaries for all
+  // extensions registered in the precedence list.
+  void LazyInit();
+
   // A cache of the highest-priority values for each preference that any
   // extension is controlling, for quick read access. Owns the stored values.
   scoped_ptr<DictionaryValue> prefs_;