MD Settings: break SettingsPageUIHandler to its own file

chrome/browser/ui/webui/settings/settings_page_ui_handler.h

+// Copyright 2016 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.
+
+#ifndef CHROME_BROWSER_UI_WEBUI_SETTINGS_SETTINGS_PAGE_UI_HANDLER_H_
+#define CHROME_BROWSER_UI_WEBUI_SETTINGS_SETTINGS_PAGE_UI_HANDLER_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "base/values.h"
+#include "content/public/browser/web_ui_message_handler.h"
+
+namespace settings {
+
+// The base class handler of Javascript messages of settings pages.
+class SettingsPageUIHandler : public content::WebUIMessageHandler {
+ public:
+  SettingsPageUIHandler();
+  ~SettingsPageUIHandler() override;
+
+  // WebUIMessageHandler implementation.
+  void RegisterMessages() override {}
+
+  // TODO(dbeam): move to WebUIMessageHandler?
+  virtual void RenderViewReused() {}
+
+ protected:
+  // Helper method for responding to JS requests initiated with
+  // cr.sendWithPromise(), for the case where the returned promise should be
+  // resolved (request succeeded).
+  void ResolveJavascriptCallback(const base::Value& callback_id,
+                                 const base::Value& response);
+
+  // Helper method for responding to JS requests initiated with
+  // cr.sendWithPromise(), for the case where the returned promise should be
+  // rejected (request failed).
+  void RejectJavascriptCallback(const base::Value& callback_id,
+                                const base::Value& response);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SettingsPageUIHandler);
+};
+
+}  // namespace settings
+
+#endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_SETTINGS_PAGE_UI_HANDLER_H_