title: Web API cannot resolve symbol Http in System.Web.Http, what is missing?
body: <p>I have a webforms project.<br>
  I use nuget to install web API by running <code>Install-Package WebApi.All</code><br>
  I create a class </p>
  
  <pre><code>public class CartController : System.Web.Http.ApiController
  </code></pre>
  
  <p>but it cannot resolve symbol Http in System.Web.Http, what dependency am I missing?</p>