[Plot] Add placeholder specs

Add placeholder specs for new scripts introduced to support
merging real-time and historical telemetry, WTD-806.

platform/features/plot/test/elements/PlotLineSpec.js

@@ -0,0 +1,12 @@
+/*global define,Promise,describe,it,expect,beforeEach,waitsFor,jasmine*/
+
+define(
+    ["../../src/elements/PlotLine"],
+    function (PlotLine) {
+        "use strict";
+
+        describe("A plot line", function () {
+
+        });
+    }
+);