title: How to cancel webRequest silently in chrome extension
body: <p>I'm re-posting my question from Chromium-extensions google group here.</p>
  
  <p>In my extension, I want to cancel some webRequests based on url pattern. My problem is that, if I return <strong>{cancel:true}</strong> in the <strong>onBeforeRequest</strong> event listener, the browser would redirect to a page telling me that the request is blocked by some extension. But I just want to cancel the request silently(as nothing happened).</p>
  
  <p>I have also tried to return <strong>{redirectUrl:""}</strong> in the <strong>onBeforeRequest</strong> event listener, the console would log an error saying that "" was not a valid URL, and a bar appeared at the bottom of the browser, saying "<strong>Waiting for extension</strong>". To dismiss that bar, I then run content script "<strong>window.stop()</strong>" in that web page. That works sometimes, but not always. So I wonder if someone has any better solution. Thanks!!</p>