content: convert user action notification to observer usage

chrome/browser/ui/webui/user_actions/user_actions_ui_handler.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/user_actions/user_actions_ui_handler.h"
 
-#include "base/logging.h"
 #include "base/values.h"
-#include "content/public/browser/notification_details.h"
-#include "content/public/browser/notification_service.h"
-#include "content/public/browser/notification_source.h"
-#include "content/public/browser/notification_types.h"
 #include "content/public/browser/web_ui.h"
 
-UserActionsUIHandler::UserActionsUIHandler() : NotificationObserver() {
-  registrar_.Add(this,
-                 content::NOTIFICATION_USER_ACTION,
-                 content::NotificationService::AllSources());
+UserActionsUIHandler::UserActionsUIHandler() {
 }
 
 UserActionsUIHandler::~UserActionsUIHandler() {
 }
 
-void UserActionsUIHandler::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
-  DCHECK_EQ(type, content::NOTIFICATION_USER_ACTION);
-  base::StringValue user_action_name(
-      *content::Details<const char*>(details).ptr());
+void UserActionsUIHandler::UserAction(const std::string& action) {
+  base::StringValue user_action_name(action);
   web_ui()->CallJavascriptFunction("userActions.observeUserAction",
                                    user_action_name);
 }
 
 void UserActionsUIHandler::RegisterMessages() {}