title: Adding custom header to WebView by adding headers to WebResourceRequest's headers in shouldInterceptRequest doesn't work
body: <p>I need to add a custom header to a page loading in WebView, but it doesn't work, header is not set:</p>
  
  <pre><code>@Override
  public WebResourceResponse shouldInterceptRequest (WebView view,  WebResourceRequest request)
  {
      request.getRequestHeaders().add("MyHeader","MyValue"); 
      return super.shouldInterceptRequest(view, request);
  }
  </code></pre>
  
  <p>What I am doing wrong here? I'm running on Android 5.</p>
  
  <p>I've seen many answers on SO saying that you have to do the HTTP request and return <code>WebResourceResponse</code> yourself. Is this because even if you modify headers like I do, they are ignored?</p>
  
  <p>I also trying to find the location in the Android source code of the call to 
  Where is the location of the call to the shouldInterceptRequest so I can see how it works myself, but I couldn't find it.</p>