[Fixed Position] Add proxy object

Add proxy object to represent the selection of the fixed position
view itself, WTD-879.

platform/features/layout/src/FixedController.js

@@ -1,8 +1,8 @@
 /*global define*/
 
 define(
-    ['./LayoutDrag'],
+    ['./LayoutDrag', './LayoutSelection', './FixedProxy'],
-    function (LayoutDrag) {
+    function (LayoutDrag, LayoutSelection, FixedProxy) {
         "use strict";
 
         var DEFAULT_DIMENSIONS = [ 2, 1 ],
@@ -26,7 +26,8 @@ define(
                 values = {},
                 cellStyles = [],
                 rawPositions = {},
-                positions = {};
+                positions = {},
+                selection;
 
             // Utility function to copy raw positions from configuration,
             // without writing directly to configuration (to avoid triggering
@@ -179,6 +180,14 @@ define(
                 populatePosition(id);
             }
 
+            //  Track current selection state
+            if (Array.isArray($scope.selection)) {
+                selection = new LayoutSelection(
+                    $scope.selection,
+                    new FixedProxy($scope.configuration)
+                );
+            }
+
             // Position panes when the model field changes
             $scope.$watch("model.composition", updateComposition);
 
@@ -194,14 +203,6 @@ define(
             // Initialize styles (position etc.) for cells
             refreshCellStyles();
 
-            if (Array.isArray($scope.selection)) {
-                $scope.selection.push({
-                    add: function () {
-                        window.alert("Placeholder; not yet implemented");
-                    }
-                });
-            }
-
             return {
                 /**
                  * Get styles for all background cells, as will populate the

platform/features/layout/src/FixedProxy.js

@@ -0,0 +1,26 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * Proxy for configuring a fixed position view via the toolbar.
+         * @constructor
+         * @param configuration the view configuration object
+         */
+        function FixedProxy(configuration) {
+            return {
+                /**
+                 * Add a new visual element to this view.
+                 */
+                add: function (type) {
+                    window.alert("Placeholder. Should add a " + type + ".");
+                }
+            };
+        }
+
+        return FixedProxy;
+    }
+);