docs(cheatsheet): add Dart-specific syntax & headings

Closes #5756

modules/angular2/docs/cheatsheet/routing.md

@@ -2,17 +2,22 @@
 Routing and navigation
 @cheatsheetIndex 10
 @description
-`import {RouteConfig, ROUTER_DIRECTIVES, ROUTER_PROVIDERS, ...} from 'angular2/router';`
+{@target js ts}`import {RouteConfig, ROUTER_DIRECTIVES, ROUTER_PROVIDERS, ...} from 'angular2/router';`{@endtarget}
+{@target dart}`import 'package:angular2/angular2.dart';`{@endtarget}
 
 
 @cheatsheetItem
-syntax:
+syntax(js ts):
 `@RouteConfig([
   { path: '/:myParam', component: MyComponent, as: 'MyCmp' },
   { path: '/staticPath', component: ..., as: ...},
   { path: '/*wildCardParam', component: ..., as: ...}
 ])
 class MyComponent() {}`|`@RouteConfig`
+syntax(dart):
+`@RouteConfig(const [
+  const Route(path: '/:myParam', component: MyComponent, name: 'MyCmp' ),
+])`
 description:
 Configures routes for the decorated component. Supports static, parameterized and wildcard routes.
 
@@ -32,8 +37,10 @@ Creates a link to a different view based on a route instruction consisting of a
 
 
 @cheatsheetItem
-syntax:
+syntax(js ts):
 `@CanActivate(() => { ... })class MyComponent() {}`|`@CanActivate`
+syntax(dart):
+`@CanActivate(() => ...)class MyComponent() {}`|`@CanActivate`
 description:
 A component decorator defining a function that the router should call first to determine if it should activate this component. Should return a boolean or a promise.
 
@@ -70,4 +77,4 @@ The router calls the routerCanDeactivate methods (if defined) of every component
 syntax:
 `routerOnDeactivate(nextInstruction, prevInstruction) { ... }`|`routerOnDeactivate`
 description:
-Called before the directive is removed as the result of a route change. May return a promise that pauses removing the directive until the promise resolves.
+Called before the directive is removed as the result of a route change. May return a promise that pauses removing the directive until the promise resolves.