title: Can't find how to use HttpContent
body: <p>I am trying to use <code>HttpContent</code>:</p>
  
  <pre><code>HttpContent myContent = HttpContent.Create(SOME_JSON);
  </code></pre>
  
  <p>...but I am not having any luck finding the DLL where it is defined.</p>
  
  <p>First, I tried adding references to <code>Microsoft.Http</code> as well as <code>System.Net</code>, but neither is in the list. I also tried adding a reference to <code>System.Net.Http</code> but the <code>HttpContent</code> class is not available.</p>
  
  <p>So, can anyone tell me where I can find the <code>HttpContent</code> class?</p>