[Fixed Position] Add fill properties

Add 'fill' properties, to allow specifying background
color in Fixed Position view. WTD-881.

platform/features/layout/src/elements/BoxProxy.js

@@ -0,0 +1,40 @@
+/*global define*/
+
+define(
+    ['./ElementProxy', './AccessorMutator'],
+    function (ElementProxy, AccessorMutator) {
+        'use strict';
+
+        /**
+         * Selection proxy for Box elements in a fixed position view.
+         * Also serves as a superclass for Text elements, since those
+         * elements have a superset of Box properties.
+         *
+         * Note that arguments here are meant to match those expected
+         * by `Array.prototype.map`
+         *
+         * @constructor
+         * @param element the fixed position element, as stored in its
+         *        configuration
+         * @param index the element's index within its array
+         * @param {Array} elements the full array of elements
+         */
+        function BoxProxy(element, index, elements) {
+            var proxy = new ElementProxy(element, index, elements);
+
+            /**
+             * Get/set this element's fill color. (Omitting the
+             * argument makes this act as a getter.)
+             * @method
+             * @memberof BoxProxy
+             * @param {string} fill the new fill color
+             * @returns {string} the fill color
+             */
+            proxy.fill = new AccessorMutator(element, 'fill');
+
+            return proxy;
+        }
+
+        return BoxProxy;
+    }
+);

platform/features/layout/src/elements/TelemetryProxy.js

@@ -1,16 +1,26 @@
 /*global define*/
 
 define(
-    ['./ElementProxy'],
-    function (ElementProxy) {
+    ['./TextProxy', './AccessorMutator'],
+    function (TextProxy, AccessorMutator) {
         'use strict';
 
         /**
+         * Selection proxy for telemetry elements in a fixed position view.
          *
+         * Note that arguments here are meant to match those expected
+         * by `Array.prototype.map`
+         *
+         * @constructor
+         * @param element the fixed position element, as stored in its
+         *        configuration
+         * @param index the element's index within its array
+         * @param {Array} elements the full array of elements
          */
         function TelemetryProxy(element, index, elements) {
-            var proxy = new ElementProxy(element, index, elements);
+            var proxy = new TextProxy(element, index, elements);
 
+            // Expose the domain object identifier
             proxy.id = element.id;
 
             return proxy;

platform/features/layout/src/elements/TextProxy.js

@@ -0,0 +1,28 @@
+/*global define*/
+
+define(
+    ['./BoxProxy', './AccessorMutator'],
+    function (BoxProxy, AccessorMutator) {
+        'use strict';
+
+        /**
+         * Selection proxy for Text elements in a fixed position view.
+         *
+         * Note that arguments here are meant to match those expected
+         * by `Array.prototype.map`
+         *
+         * @constructor
+         * @param element the fixed position element, as stored in its
+         *        configuration
+         * @param index the element's index within its array
+         * @param {Array} elements the full array of elements
+         */
+        function TextProxy(element, index, elements) {
+            var proxy = new BoxProxy(element, index, elements);
+
+            return proxy;
+        }
+
+        return TextProxy;
+    }
+);