refactor(router): move assertComponentExists into facade

This is to make way for a refactor to the ng 1.x router directives,
which will use strings rather than controller functions in route configs.

modules/angular2/src/router/route_config_nomalizer.dart

@@ -1,7 +1,14 @@
 library angular2.src.router.route_config_normalizer;
 
 import "route_config_decorator.dart";
+import "package:angular2/src/core/facade/exceptions.dart" show BaseException;
 
 RouteDefinition normalizeRouteConfig(RouteDefinition config) {
   return config;
 }
+
+void assertComponentExists(Type component, String path) {
+  if (component == null) {
+    throw new BaseException('Component for route "${path}" is not defined, or is not a class.');
+  }
+}

modules/angular2/src/router/route_config_nomalizer.ts

@@ -1,6 +1,6 @@
 import {AsyncRoute, AuxRoute, Route, Redirect, RouteDefinition} from './route_config_decorator';
 import {ComponentDefinition} from './route_definition';
-import {Type} from 'angular2/src/core/facade/lang';
+import {isType, Type} from 'angular2/src/core/facade/lang';
 import {BaseException, WrappedException} from 'angular2/src/core/facade/exceptions';
 
 
@@ -47,3 +47,9 @@ export function normalizeRouteConfig(config: RouteDefinition): RouteDefinition {
 
   return config;
 }
+
+export function assertComponentExists(component: Type, path: string): void {
+  if (!isType(component)) {
+    throw new BaseException(`Component for route "${path}" is not defined, or is not a class.`);
+  }
+}

modules/angular2/src/router/route_registry.ts

@@ -31,7 +31,7 @@ import {
 } from './route_config_impl';
 import {reflector} from 'angular2/src/core/reflection/reflection';
 import {Injectable} from 'angular2/src/core/di';
-import {normalizeRouteConfig} from './route_config_nomalizer';
+import {normalizeRouteConfig, assertComponentExists} from './route_config_nomalizer';
 import {parser, Url, pathSegmentsToUrl} from './url_parser';
 
 var _resolveToNull = PromiseWrapper.resolve(null);
@@ -318,9 +318,3 @@ function assertTerminalComponent(component, path) {
     }
   }
 }
-
-function assertComponentExists(component: Type, path: string): void {
-  if (!isType(component)) {
-    throw new BaseException(`Component for route "${path}" is not defined, or is not a class.`);
-  }
-}