st-theme-node: Add repeating backgrounds

Add support for the CSS "background-repeat" property. Currently, this
only supports on/off, rather than allowing tiling in each individual
dimension. It is supported for both the cogl and cairo rendering paths.

https://bugzilla.gnome.org/show_bug.cgi?id=680801

tests/interactive/background-repeat.js

@@ -0,0 +1,29 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+
+const Clutter = imports.gi.Clutter;
+const St = imports.gi.St;
+
+const UI = imports.testcommon.ui;
+
+function test() {
+    let stage = new Clutter.Stage({ width: 640, height: 480 });
+    UI.init(stage);
+
+    let vbox = new St.BoxLayout({ width: stage.width,
+                                  height: stage.height,
+                                  style: 'background: #ffee88;' });
+    stage.add_actor(vbox);
+
+    let scroll = new St.ScrollView();
+    vbox.add(scroll, { expand: true });
+
+    let box = new St.BoxLayout({ vertical: true });
+    scroll.add_actor(box);
+
+    let contents = new St.Widget({ width: 1000, height: 1000,
+                                   style_class: 'background-image background-repeat' });
+    box.add_actor(contents);
+
+    UI.main(stage);
+}
+test();