[Core] Add throttle service

Add service for throttling function calls; specifically supports
reducing tick mark recalculation, WTD-1202.

platform/core/test/services/ThrottleSpec.js

@@ -0,0 +1,49 @@
+/*global define,Promise,describe,it,expect,beforeEach,waitsFor,jasmine*/
+
+define(
+    ["../../src/services/Throttle"],
+    function (Throttle) {
+        "use strict";
+
+        describe("The 'throttle' service", function () {
+            var throttle,
+                mockTimeout,
+                mockFn,
+                mockPromise;
+            
+            beforeEach(function () {
+                mockTimeout = jasmine.createSpy("$timeout");
+                mockPromise = jasmine.createSpyObj("promise", ["then"]);
+                mockFn = jasmine.createSpy("fn");
+                mockTimeout.andReturn(mockPromise);
+                throttle = new Throttle(mockTimeout);
+            });
+            
+            it("provides functions which run on a timeout", function () {
+                var throttled = throttle(mockFn);
+                // Verify precondition: Not called at throttle-time
+                expect(mockTimeout).not.toHaveBeenCalled();
+                expect(throttled()).toEqual(mockPromise);
+                expect(mockTimeout).toHaveBeenCalledWith(mockFn, 0, false);
+            });
+            
+            it("schedules only one timeout at a time", function () {
+                var throttled = throttle(mockFn);
+                throttled();
+                throttled();
+                throttled();
+                expect(mockTimeout.calls.length).toEqual(1);
+            });
+            
+            it("schedules additional invocations after resolution", function () {
+                var throttled = throttle(mockFn);
+                throttled();
+                mockPromise.then.mostRecentCall.args[0](); // Resolve timeout
+                throttled();
+                mockPromise.then.mostRecentCall.args[0]();
+                throttled();
+                expect(mockTimeout.calls.length).toEqual(3);
+            });
+        });
+    }
+);