<pattern> tag attribute "patternUnits" should be supported

[nhunzaker]

patternUnits is really useful for SVG patterns, but it doesn't appear to be transferred to the DOM when I render a component that uses it. Given the following sample SVG,

<svg version="1.1" height="200" width="200">
  <defs>
    <pattern id="scanlines" width="5" height="5" patternUnits="userSpaceOnUse">
      <svg width="5" height="5">
        <rect width="5" height="5" fill="#000"></rect>
        <path d="M0 5L5 0ZM6 4L4 6ZM-1 1L1 -1Z" stroke="#fff" strokeWidth="2"></path>
      </svg>
    </pattern>
  </defs>
  <circle r="100" cx="100" cy="100" fill="url(#scanlines)" />
</svg>

The result should display a scan line pattern, as demonstrated here (in raw SVG):

http://codepen.io/nhunzaker/pen/idzCq?editors=100

However this doesn't happen because the patternUnits attribute is never transferred. Note the missing patternUnits attribute within pattern#scanlines. This is the result of executing React.renderComponentToString on this svg markup:

<svg version="1.1" height="200" width="200" data-reactid=".0" data-react-checksum="750163038">
    <defs data-reactid=".0.0">
        <pattern id="scanlines" width="5" height="5" data-reactid=".0.0.0">
            <svg width="5" height="5" data-reactid=".0.0.0.0">
                <rect width="5" height="5" fill="#000" data-reactid=".0.0.0.0.0"></rect>
                <path d="M0 5L5 0ZM6 4L4 6ZM-1 1L1 -1Z" stroke="#fff" stroke-width="2" data-reactid=".0.0.0.0.1"></path>
            </svg>
        </pattern>
    </defs>
    <circle r="100" cx="100" cy="100" fill="url(#scanlines)" data-reactid=".0.1"></circle
</svg>

[sophiebits]

Closing in favor of #1657.