docs: function getExtensionWithKnownPrefixes(gl, name) {
      for (var ii = 0; ii < browserPrefixes.length; ++ii) {
        var prefixedName = browserPrefixes[ii] + name;
        var ext = gl.getExtension(prefixedName);
        if (ext) {
          return ext;
        }
      }
      return undefined;
    }