Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/extensions/api/storage/settings_storage_factory.h

Index: chrome/browser/extensions/api/storage/settings_storage_factory.h
diff --git a/chrome/browser/extensions/api/storage/settings_storage_factory.h b/chrome/browser/extensions/api/storage/settings_storage_factory.h
index 7fd28cf0862bb62cc6851ab8b14d11f20328a109..86c8b8bdb09588ba463ba58963b2246690ef07f0 100644
--- a/chrome/browser/extensions/api/storage/settings_storage_factory.h
+++ b/chrome/browser/extensions/api/storage/settings_storage_factory.h
@@ -26,6 +26,12 @@ class SettingsStorageFactory
   virtual ValueStore* Create(const base::FilePath& base_path,
                              const std::string& extension_id) = 0;
 
+  // Deletes the database for the extension, if one exists.
+  // Note: it is important to delete references to the database if any are
+  // held, because ValueStores will create themselves if there is no file.
+  virtual void DeleteDatabaseIfExists(const base::FilePath& base_path,
+                                      const std::string& extension_id) = 0;
+
  protected:
   friend class base::RefCountedThreadSafe<SettingsStorageFactory>;
   virtual ~SettingsStorageFactory() {}