keyboardmanager: Apply desired backend's keymap accordingly

Follow "org.gnome.desktop.input-sources" as needed and tweak it to comply
with non-latin layouts as well.

src/KeyboardManager.vala

@@ -0,0 +1,87 @@
+//
+//  Copyright (C) 2016 Santiago León
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+namespace Gala
+{
+	public class KeyboardManager : Object
+	{
+		static KeyboardManager? instance;
+		static VariantType sources_variant_type;
+
+		public static void init ()
+		{
+			if (instance == null) {
+				instance = new KeyboardManager ();
+			}
+		}
+
+		static construct
+		{
+			sources_variant_type = new VariantType ("a(ss)");
+		}
+
+		GLib.Settings settings;
+
+		KeyboardManager ()
+		{
+			Object ();
+		}
+		
+		construct
+		{
+			var schema = GLib.SettingsSchemaSource.get_default ().lookup ("org.gnome.desktop.input-sources", true);
+			return_if_fail (schema != null);
+			
+			settings = new GLib.Settings.full (schema, null, null);
+			Signal.connect (settings, "changed", (Callback) set_keyboard_layout, this);
+		}
+
+		[CCode (instance_pos = -1)]
+		void set_keyboard_layout (GLib.Settings settings, string key)
+		{
+			if (!(key == "current" || key == "source" || key == "xkb-options"))
+				return;
+
+			string layout = "us", variant = "", options = "";
+
+			var sources = settings.get_value ("sources");
+			return_if_fail (sources.is_of_type (sources_variant_type));
+
+			var current = settings.get_uint ("current");
+			var child = sources.get_child_value (current);
+			unowned string type, name;
+			child.get ("(&s&s)", out type, out name);
+			if (type == "xkb") {
+				string[] arr = name.split ("+", 2);
+				layout = arr[0];
+				variant = arr[1] ?? "";
+			}
+
+			var xkb_options = settings.get_strv ("xkb-options");
+			if (xkb_options.length > 0)
+				options = string.joinv (",", xkb_options);
+
+			// Needed to make common keybindings work on non-latin layouts
+			if (layout != "us" || variant != "") {
+				layout = layout + ",us";
+				variant = variant + ",";
+			}
+
+			Meta.Backend.get_backend ().set_keymap (layout, variant, options);
+		}
+	}
+}

src/Makefile.am

@@ -36,6 +36,7 @@ gala_VALASOURCES = \
 	DockThemeManager.vala \
 	DragDropAction.vala \
 	InternalUtils.vala \
+	KeyboardManager.vala \
 	Main.vala \
 	PluginManager.vala \
 	ScreenSaver.vala \

src/WindowManager.vala

@@ -141,6 +141,7 @@ namespace Gala
 			DBusAccelerator.init (this);
 #endif
 			WindowListener.init (screen);
+			KeyboardManager.init ();
 
 			// Due to a bug which enables access to the stage when using multiple monitors
 			// in the screensaver, we have to listen for changes and make sure the input area