Properly initialize <Router> state after match

[morlay]

Since could through the renderProps to Router
https://github.com/rackt/react-router/blob/v2.0.0-rc5/modules/Router.js#L46
we could use match on client like this ? (should this correct ? )

import React from 'react'
import { render } from 'react-dom'
import { match, Router, browserHistory as history } from 'react-router'

class App extends React.Component {
  render() {
    console.log(this.context.router.isActive('/about')); // false on first render
    return (
      <div>
        <h1>App</h1>
        {this.props.children}
      </div>
    )
  }
}

App.contextTypes = {
  router: React.PropTypes.object
};

const routes = {
  path: '/',
  component: App,
  childRoutes: [
    {
      path: '/about',
      component: App,
      onEnter: (nextState, replace, callback) => {
        setTimeout(() => {
          callback()
        }, 1000)
      }
    }
  ]
};

const { pathname, search, hash } = window.location;
const location = `${pathname}${search}${hash}`;

match({
  routes,
  location,
  history
}, (error, redirectLocation, renderProps) => {
  console.log(renderProps.router.isActive('/about')); // return true
  render(
    <Router
      {...renderProps}
      history={history} // if pass renderProps.history, well show `router.history` warning.
    />,
    document.getElementById('app')
  )
});

However, �
If an async method in onEnter,
The router in Router will re-initial, and the router.isActive will return false, until onEnter callback, and re-render the Router. ( see the console.log in code, above)

This may break lazy match in client.
And in server render, The Link active state, will be different between client and server.

[taion]

Let's track this on #2965 – the fix is a bit broader than what's described here.