Made notification center notifications collapsed and expandable.

ui/message_center/message_center.cc

Index: ui/message_center/message_center.cc
diff --git a/ui/message_center/message_center.cc b/ui/message_center/message_center.cc
index 8aeb89b0611dda4c5ff53d318605f84e9992a82f..348e79e69f543568eaf0bed9bc265d1b1131cc0e 100644
--- a/ui/message_center/message_center.cc
+++ b/ui/message_center/message_center.cc
@@ -103,7 +103,7 @@ void MessageCenter::SetNotificationButtonIcon(
 }
 
 //------------------------------------------------------------------------------
-// Overridden from NotificationList::Delegate.
+// Overridden from NotificationList::Delegate:
 
 void MessageCenter::SendRemoveNotification(const std::string& id,
                                            bool by_user) {
@@ -160,10 +160,6 @@ void MessageCenter::OnNotificationClicked(const std::string& id) {
   }
 }
 
-void MessageCenter::OnQuietModeChanged(bool quiet_mode) {
-  NotifyMessageCenterChanged(true);
-}
-
 void MessageCenter::OnButtonClicked(const std::string& id, int button_index) {
   if (delegate_)
     delegate_->OnButtonClicked(id, button_index);
@@ -173,8 +169,12 @@ void MessageCenter::OnButtonClicked(const std::string& id, int button_index) {
   }
 }
 
-NotificationList* MessageCenter::GetNotificationList() {
-  return notification_list_.get();
+void MessageCenter::OnExpand(const std::string& id) {
+  notification_list_->MarkNotificationAsExpanded(id);
+}
+
+void MessageCenter::OnQuietModeChanged(bool quiet_mode) {
+  NotifyMessageCenterChanged(true);
 }
 
 void MessageCenter::Delegate::OnButtonClicked(const std::string& id,