title: why change the left of an element with matrix3d won't trigger repaint
body: <p>It is a bit difficult to describe, so I split it into several steps:</p>
  
  <ol>
  <li>I open the <code>Show paint rectangles</code> option on chrome <strong>DevTool</strong>.</li>
  <li>I open a web page find an element, and change the left or top property of the element.</li>
  <li>I can see the element move and a green rectangle appears on the element.</li>
  <li>I find another element with a CSS property "transform" and value.</li>
  </ol>
  
  <blockquote>
    <p>matrix3d(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);</p>
  </blockquote>
  
  <ol start="5">
  <li>I change this element's left and top.</li>
  <li>I can still see the element move, but there is not a green rectangle appear on this element.Maybe that means the moving of the element did't trigger repainting of the page.</li>
  </ol>
  
  <p>What's more, when I change the "opacity" of the element, the same thing happens too.</p>
  
  <p>So why is the <code>matrix3d</code> prevent the repaint ?</p>
  
  <p>I have watched this video:<a href="http://www.paulirish.com/2012/why-moving-elements-with-translate-is-better-than-posabs-topleft/" rel="nofollow">Why Moving Elements With Translate() Is Better Than Pos:abs Top/left</a>, it seems that changing of "left" and "top" are not handled by GPU.So I'm confused.</p>