Include the notifySplices method, and also add a trivial test for the

ArraySplice function with mutable and immutable arrays.

types/polymer/index.d.ts

@@ -139,6 +139,8 @@ declare global {
 
       unshift?(path: string, ...item: any[]): number;
 
+      notifySplices?(path: string, splices: ReadonlyArray<polymer.PolymerSplice>): void;
+
       // ResolveUrl
 
       resolveUrl?(url: string): string;

types/polymer/polymer-tests.ts

@@ -82,3 +82,11 @@ class MyElement3 implements polymer.Base {
 }
 
 Polymer(MyElement3);
+
+// Test splice computation
+const splices: polymer.PolymerSplice[] = Polymer.ArraySplice.calculateSplices(
+  [1,2,3], [1,2]);
+
+// Test that readonly arrays also work.
+const splices2: polymer.PolymerSplice[] = Polymer.ArraySplice.calculateSplices(
+  Object.freeze([1,2,3]), Object.freeze([1,2]));