title: Stream stream = WriteableBitmap.PixelBuffer.AsStream() missing
body: <p>I'm writing windows store app (8.1) and I have sample (probably for win 8.0): </p>
  
  <pre><code>private WriteableBitmap WriteableBitmap;
  …
  WriteableBitmap = new WriteableBitmap(500,500);
  …
  using (Stream stream = WriteableBitmap.PixelBuffer.AsStream())
  {
      …
  }
  </code></pre>
  
  <p>So I have created new win 8.1 project and trying to do it same way, but when I get to:</p>
  
  <pre><code>using (Stream stream = WriteableBitmap.PixelBuffer.AsStream())
  </code></pre>
  
  <p>My project dont recognize <code>*.AsStream()</code> method, can anyone tell me why?</p>