Introduce a new API to handle native notification clicks

chrome/browser/notifications/notification_common.h

Index: chrome/browser/notifications/notification_common.h
diff --git a/chrome/browser/notifications/notification_common.h b/chrome/browser/notifications/notification_common.h
index 79ac93ebffe6e77057bb525b6bcc6a057183d2c4..280c84df461e0fe43a28fa0c4751d4f758392a2b 100644
--- a/chrome/browser/notifications/notification_common.h
+++ b/chrome/browser/notifications/notification_common.h
@@ -20,6 +20,13 @@ class NotificationCommon {
     OPERATION_MAX = SETTINGS
   };
 
+  // Possible kinds of notifications
+  enum Type {
+    PERSISTENT = 0,
+    NON_PERSISTENT = 1,
+    TYPE_MAX = NON_PERSISTENT
+  };
+
   // Open the Notification settings screen when clicking the right button.
   // TODO(miguelg) have it take a Profile instead once NotificationObjectProxy
   // is updated.