Adding client code for new desktop First Run Experience.

chrome/browser/ui/webui/welcome_ui.h

Index: chrome/browser/ui/webui/welcome_ui.h
diff --git a/chrome/browser/ui/webui/welcome_ui.h b/chrome/browser/ui/webui/welcome_ui.h
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+++ b/chrome/browser/ui/webui/welcome_ui.h
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+// Copyright (c) 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_WELCOME_UI_H_
+#define CHROME_BROWSER_UI_WEBUI_WELCOME_UI_H_
+
+#include "content/public/browser/web_ui_controller.h"
+#include "url/gurl.h"
+
+// The WebUI for chrome://welcome, the page which greets new Desktop users and
+// promotes sign-in.
+
+class WelcomeUI : public content::WebUIController {
+ public:
+  explicit WelcomeUI(content::WebUI* web_ui, const GURL& url);
+  ~WelcomeUI() override;
+};
+
+#endif  // CHROME_BROWSER_UI_WEBUI_WELCOME_UI_H_