Implement intro wrap for new settings.

Telegram/SourceFiles/settings/settings_intro.h

@@ -0,0 +1,51 @@
+/*
+This file is part of Telegram Desktop,
+the official desktop application for the Telegram messaging service.
+
+For license and copyright information please follow this link:
+https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
+*/
+#pragma once
+
+#include "window/layer_widget.h"
+
+namespace Ui {
+class VerticalLayout;
+class FadeShadow;
+class FlatLabel;
+template <typename Widget>
+class FadeWrap;
+} // namespace Ui
+
+namespace Settings {
+
+class IntroWidget;
+
+class LayerWidget : public Window::LayerWidget {
+public:
+	LayerWidget(QWidget*);
+
+	void showFinished() override;
+	void parentResized() override;
+
+	static int MinimalSupportedWidth();
+
+protected:
+	int resizeGetHeight(int newWidth) override;
+	void doSetInnerFocus() override;
+
+	void paintEvent(QPaintEvent *e) override;
+
+private:
+	void setupHeightConsumers();
+
+	object_ptr<IntroWidget> _content;
+
+	int _desiredHeight = 0;
+	bool _inResize = false;
+	bool _tillTop = false;
+	bool _tillBottom = false;
+
+};
+
+} // namespace Info