[Fixed Position] Add button to show/hide telemetry name

Add button to show/hide name of telemetry elements in
fixed position view, WTD-881.

platform/features/layout/src/FixedController.js

@@ -195,6 +195,7 @@ define(
                     id: id,
                     stroke: "transparent",
                     color: "#717171",
+                    titled: true,
                     width: DEFAULT_DIMENSIONS[0],
                     height: DEFAULT_DIMENSIONS[1]
                 });

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

@@ -5,6 +5,9 @@ define(
     function (TextProxy, AccessorMutator) {
         'use strict';
 
+        // Method names to expose from this proxy
+        var HIDE = 'hideTitle', SHOW = 'showTitle';
+
         /**
          * Selection proxy for telemetry elements in a fixed position view.
          *
@@ -20,9 +23,27 @@ define(
         function TelemetryProxy(element, index, elements) {
             var proxy = new TextProxy(element, index, elements);
 
+            // Toggle the visibility of the title
+            function toggle() {
+                // Toggle the state
+                element.titled = !element.titled;
+
+                // Change which method is exposed, to influence
+                // which button is shown in the toolbar
+                delete proxy[SHOW];
+                delete proxy[HIDE];
+                proxy[element.titled ? HIDE : SHOW] = toggle;
+            }
+
             // Expose the domain object identifier
             proxy.id = element.id;
 
+            // Expose initial toggle
+            proxy[element.titled ? HIDE : SHOW] = toggle;
+
+            // Don't expose text configuration
+            delete proxy.text;
+
             return proxy;
         }