StScrollView: Implement real fade effect

Implement an edge fade effect (top/bottom) using a
ClutterOffscreenEffect subclass, replacing the former
shadow hack.

https://bugzilla.gnome.org/show_bug.cgi?id=639460

src/st/st-scroll-view-fade.h

@@ -0,0 +1,40 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+/*
+ * st-scroll-view-fade.h: Edge fade effect for StScrollView
+ *
+ * Copyright 2010 Intel Corporation.
+ * Copyright 2011 Adel Gadllah
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU Lesser General Public License,
+ * version 2.1, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __ST_SCROLL_VIEW_FADE_H__
+#define __ST_SCROLL_VIEW_FADE_H__
+
+#include <clutter/clutter.h>
+
+G_BEGIN_DECLS
+
+#define ST_TYPE_SCROLL_VIEW_FADE        (st_scroll_view_fade_get_type ())
+#define ST_SCROLL_VIEW_FADE(obj)        (G_TYPE_CHECK_INSTANCE_CAST ((obj), ST_TYPE_SCROLL_VIEW_FADE, StScrollViewFade))
+#define ST_IS_SCROLL_VIEW_FADE(obj)     (G_TYPE_CHECK_INSTANCE_TYPE ((obj), ST_TYPE_SCROLL_VIEW_FADE))
+
+typedef struct _StScrollViewFade       StScrollViewFade;
+
+GType st_scroll_view_fade_get_type (void) G_GNUC_CONST;
+
+ClutterEffect *st_scroll_view_fade_new (void);
+
+G_END_DECLS
+
+#endif /* __ST_SCROLL_VIEW_FADE_H__ */