fix(router): provide a top-level route segment for injection

modules/@angular/router/src/directives/router_link.ts

@@ -59,7 +59,7 @@ export class RouterLink implements OnDestroy {
   @HostBinding() href: string;
   @HostBinding('class.router-link-active') isActive: boolean = false;
 
-  constructor(@Optional() private _routeSegment: RouteSegment, private _router: Router) {
+  constructor(private _routeSegment: RouteSegment, private _router: Router) {
     // because auxiliary links take existing primary and auxiliary routes into account,
     // we need to update the link whenever params or other routes change.
     this._subscription =

modules/@angular/router/src/recognize.ts

@@ -8,7 +8,6 @@ import {ComponentResolver} from '@angular/core';
 import {DEFAULT_OUTLET_NAME} from './constants';
 import {reflector} from '@angular/core';
 
-// TODO: vsavkin: recognize should take the old tree and merge it
 export function recognize(componentResolver: ComponentResolver, rootComponent: Type,
                           url: UrlTree): Promise<RouteTree> {
   let matched = new _MatchResult(rootComponent, [url.root], {}, rootNode(url).children, []);

modules/@angular/router/src/router_providers_common.ts

@@ -1,6 +1,7 @@
 import {OpaqueToken, ComponentResolver} from '@angular/core';
 import {LocationStrategy, PathLocationStrategy, Location} from '@angular/common';
 import {Router, RouterOutletMap} from './router';
+import {RouteSegment} from './segments';
 import {RouterUrlSerializer, DefaultRouterUrlSerializer} from './router_url_serializer';
 import {ApplicationRef} from '@angular/core';
 import {BaseException} from '@angular/core';
@@ -18,6 +19,7 @@ export const ROUTER_PROVIDERS_COMMON: any[] = /*@ts2dart_const*/[
     deps: /*@ts2dart_const*/
         [ApplicationRef, ComponentResolver, RouterUrlSerializer, RouterOutletMap, Location],
   },
+  /*@ts2dart_Provider*/ {provide: RouteSegment, useFactory: (r) => r.routeTree.root, deps: [Router]}
 ];
 
 function routerFactory(app: ApplicationRef, componentResolver: ComponentResolver,

modules/@angular/router/test/integration_spec.ts

@@ -39,6 +39,7 @@ export function main() {
       provide(RouterUrlSerializer, {useClass: DefaultRouterUrlSerializer}),
       RouterOutletMap,
       provide(Location, {useClass: SpyLocation}),
+      provide(RouteSegment, {useFactory: (r) => r.routeTree.root, deps: [Router]}),
       provide(Router,
               {
                 useFactory: (resolver, urlParser, outletMap, location) => new Router(
@@ -224,6 +225,13 @@ export function main() {
 
            expect(getDOM().getAttribute(native, "href")).toEqual("/team/33/simple(aux:simple2)");
          })));
+
+      it("should support top-level link",
+        fakeAsync(inject([Router, TestComponentBuilder], (router, tcb) => {
+          let fixture = tcb.createFakeAsync(LinkCmp);
+          advance(fixture);
+          expect(fixture.debugElement.nativeElement).toHaveText('link');
+        })));
     }
   });
 }

modules/@angular/router/test/recognize_spec.ts

@@ -20,7 +20,7 @@ import {DefaultRouterUrlSerializer} from '../src/router_url_serializer';
 import {DEFAULT_OUTLET_NAME} from '../src/constants';
 
 export function main() {
-  ddescribe('recognize', () => {
+  describe('recognize', () => {
     it('should handle position args',
        inject([AsyncTestCompleter, ComponentResolver], (async, resolver) => {
          recognize(resolver, ComponentA, tree("b/paramB/c/paramC/d"))

modules/@angular/router/testing/router_testing_providers.ts

@@ -1,6 +1,7 @@
 import {SpyLocation} from '@angular/common/testing';
 import {Location} from '@angular/common';
 import {Router, RouterOutletMap} from '../src/router';
+import {RouteSegment} from '../src/segments';
 import {RouterUrlSerializer, DefaultRouterUrlSerializer} from '../src/router_url_serializer';
 import {Component, ComponentResolver} from '@angular/core';
 
@@ -24,4 +25,5 @@ export const ROUTER_FAKE_PROVIDERS: any[] = /*@ts2dart_const*/ [
     deps: /*@ts2dart_const*/
         [ComponentResolver, RouterUrlSerializer, RouterOutletMap, Location]
   },
+  /*@ts2dart_Provider*/ {provide: RouteSegment, useFactory: (r) => r.routeTree.root, deps: [Router]}
 ];