title: How to go back from web view in flutter?
body: <p>After clicking the button it should show the web view. I did this. But when press the back button it is closing the app. It does not go back to previous state. If I press back button it should go back to previous page or state. I am getting web view from a function. 
  Here is my code:</p>
  
  <pre><code>_contentSearch(BuildContext context){
     url = "https://www.google.com";
     return WebviewScaffold(
        url: url,
        appBar: AppBar(
          title: Text("Google"),
        ),
        withJavascript: true,
        withLocalStorage: true,
        withZoom: false,
        enableAppScheme: true,
      )
    },
   );
  }
  </code></pre>
  
  <p>And I am calling this method like this:</p>
  
  <pre><code> FlatButton(
          padding: EdgeInsets.all(0.0),
          onPressed: (){
            Navigator.pushReplacement(
                context,
                new MaterialPageRoute(builder: (BuildContext context) =&gt; _contentSearch(context)
                ));
          },
         child: new Text("Button"),
      ),
  </code></pre>
  
  <p>It's not going back. It's always closing the app.</p>