<!DOCTYPE html>
<html>
<title>Percentages in a mask</title>
<link rel="help"  href="https://crbug.com/1500476" />
<link rel="match"  href="mask-percentage-ref.html" />
<body>
<svg
  width="100%" height="100%"
  xmlns="http://www.w3.org/2000/svg">

  <defs>
    <mask id='corner'>
      <g><rect x="0" y="0" height="100%" width="100%" fill="white" /></g>
    </mask>
  </defs>

  <rect x="0" y="0" width="100%" height="100%" fill="red"></rect>
  <g mask='url(#corner)'>
    <rect x="0" y="0" width="100%" height="