[Representation] Add DnD service

Add service to communicate data after/during a drag-and-drop, to allow
drag contents to be checked during dragover, and to allow full JavaScript
objects to be passed during drags (within the same window.) WTD-988.

platform/representation/test/services/DndServiceSpec.js

@@ -0,0 +1,45 @@
+/*global define,Promise,describe,it,expect,beforeEach,waitsFor,jasmine*/
+
+
+define(
+    ["../../src/services/DndService"],
+    function (DndService) {
+        "use strict";
+
+        describe("The drag-and-drop service", function () {
+            var service;
+
+            beforeEach(function () {
+                var mockLog = jasmine.createSpyObj("$log", ['debug']);
+                service = new DndService(mockLog);
+            });
+
+            it("allows setting of arbitrary objects", function () {
+                var foo = {
+                    bar: function () { return 42; }
+                };
+
+                service.setData('xyz', foo);
+
+                // Test that we can get back callable data, since this is
+                // a key reason for having a service separate from HTML5 DnD.
+                expect(service.getData('xyz').bar()).toEqual(42);
+            });
+
+            it("stores data under specified keys", function () {
+                service.setData('abc', 42);
+                service.setData('def', "some data");
+
+                expect(service.getData('abc')).toEqual(42);
+                expect(service.getData('def')).toEqual("some data");
+            });
+
+            it("removes data", function () {
+                service.setData('abc', 42);
+                service.removeData('abc');
+                expect(service.getData('abc')).toBeUndefined();
+            });
+
+        });
+    }
+);