feat(pipes): add static append method to Pipes

This change allows creation of a new Pipes binding with new pipes appended
to pipes of an inherited Pipes instance.

Closes #2901

modules/angular2/test/change_detection/pipes/pipes_spec.ts

@@ -11,7 +11,9 @@ import {
   SpyPipeFactory
 } from 'angular2/test_lib';
 
+import {Injector, bind} from 'angular2/di';
 import {Pipes} from 'angular2/src/change_detection/pipes/pipes';
+import {PipeFactory} from 'angular2/src/change_detection/pipes/pipe';
 
 export function main() {
   describe("pipe registry", () => {
@@ -73,5 +75,49 @@ export function main() {
       expect(() => r.get("type", "some object"))
           .toThrowError(`Cannot find 'type' pipe supporting object 'some object'`);
     });
+
+    describe('.append()', () => {
+      it('should create a factory that appends new pipes to old', () => {
+        firstPipeFactory.spy("supports").andReturn(false);
+        secondPipeFactory.spy("supports").andReturn(true);
+        secondPipeFactory.spy("create").andReturn(secondPipe);
+        var originalPipes = new Pipes({'async': [firstPipeFactory]});
+        var binding = Pipes.append({'async':<PipeFactory[]>[secondPipeFactory]});
+        var pipes: Pipes = binding.toFactory(originalPipes);
+
+        expect(pipes.config['async'].length).toBe(2);
+        expect(originalPipes.config['async'].length).toBe(1);
+        expect(pipes.get('async', 'second plz')).toBe(secondPipe);
+      });
+
+
+      it('should append to di-inherited pipes', () => {
+        firstPipeFactory.spy("supports").andReturn(false);
+        secondPipeFactory.spy("supports").andReturn(true);
+        secondPipeFactory.spy("create").andReturn(secondPipe);
+
+        var originalPipes: Pipes = new Pipes({'async': [firstPipeFactory]});
+        var injector: Injector = Injector.resolveAndCreate([bind(Pipes).toValue(originalPipes)]);
+        var childInjector: Injector =
+            injector.resolveAndCreateChild([Pipes.append({'async': [secondPipeFactory]})]);
+        var parentPipes: Pipes = injector.get(Pipes);
+        var childPipes: Pipes = childInjector.get(Pipes);
+        expect(childPipes.config['async'].length).toBe(2);
+        expect(parentPipes.config['async'].length).toBe(1);
+        expect(childPipes.get('async', 'second plz')).toBe(secondPipe);
+      });
+
+
+      it('should throw if calling append when creating root injector', () => {
+        secondPipeFactory.spy("supports").andReturn(true);
+        secondPipeFactory.spy("create").andReturn(secondPipe);
+
+        var injector: Injector =
+            Injector.resolveAndCreate([Pipes.append({'async': [secondPipeFactory]})]);
+
+        expect(() => injector.get(Pipes))
+            .toThrowError(/Cannot append to Pipes without a parent injector/g);
+      });
+    });
   });
-}
+}