title: access the theme from outside material-ui component
body: <p>I have a theme provider using the standard dark theme. I'd like to be able to access the details of this theme from my own custom component, but I cannot figure out how that would be done. In the example below, <code>this.props.theme</code> is undefined</p>
  
  <pre><code>ReactDOM.render(
      &lt;MuiThemeProvider theme={theme}&gt;
          &lt;App/&gt;
      &lt;/MuiThemeProvider&gt;, document.getElementById('root')
  );
  
  class App extends Component {
      render() {
          const {classes} = this.props;
          return (
              &lt;div className="App"&gt;
                  &lt;MainMenu/&gt;
                  &lt;div className={classes.root}&gt;
                      &lt;Grid container spacing={8}&gt;
                          &lt;Grid item xs&gt;
                              &lt;Chart theme={this.props.theme}/&gt;
                          &lt;/Grid&gt;
                      &lt;/Grid&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
          );
      }
  }
  </code></pre>