feat(iterable_differ): support immutable lists

Closes #7127

modules/angular2/test/core/change_detection/differs/default_iterable_differ_spec.ts

@@ -31,7 +31,6 @@ class ComplexItem {
   toString() { return `{id: ${this.id}, color: ${this.color}}` }
 }
 
-// todo(vicb): UnmodifiableListView / frozen object when implemented
 export function main() {
   describe('iterable differ', function() {
     describe('DefaultIterableDiffer', function() {
@@ -314,6 +313,36 @@ export function main() {
             }));
       });
 
+      it('should not diff immutable collections if they are the same', () => {
+        // Note: Use trackBy to know if diffing happened
+        var trackByCount = 0;
+        var trackBy = (index: number, item: any): any => {
+          trackByCount++;
+          return item;
+        };
+        var differ = new DefaultIterableDiffer(trackBy);
+        var l1 = ListWrapper.createImmutable([1]);
+
+        differ.check(l1);
+        expect(trackByCount).toBe(1);
+        expect(differ.toString())
+            .toEqual(
+                iterableChangesAsString({collection: ['1[null->0]'], additions: ['1[null->0]']}));
+
+
+        trackByCount = 0;
+        differ.check(l1);
+        expect(trackByCount).toBe(0);
+        expect(differ.toString())
+            .toEqual(iterableChangesAsString({collection: ['1'], previous: ['1']}));
+
+        trackByCount = 0;
+        differ.check(l1);
+        expect(trackByCount).toBe(0);
+        expect(differ.toString())
+            .toEqual(iterableChangesAsString({collection: ['1'], previous: ['1']}));
+      });
+
       describe('diff', () => {
         it('should return self when there is a change',
            () => { expect(differ.diff(['a', 'b'])).toBe(differ); });