code: function installNoFocusLibs(profileDir) {
    var x86 = path.join(profileDir, 'x86');
    var amd64 = path.join(profileDir, 'amd64');
  
    return mkdir(x86)
        .then(copyLib.bind(null, NO_FOCUS_LIB_X86, x86))
        .then(mkdir.bind(null, amd64))
        .then(copyLib.bind(null, NO_FOCUS_LIB_AMD64, amd64))
        .then(function() {
          return x86 + ':' + amd64;
        });
  
    function mkdir(dir) {
      return io.exists(dir).then(function(exists) {
        if (!exists) {
          return promise.checkedNodeCall(fs.mkdir, dir);
        }
      });
    }
  
    function copyLib(src, dir) {
      return io.copy(src, path.join(dir, X_IGNORE_NO_FOCUS_LIB));
    }
  }
docs: Copies the no focus libs into the given profile directory.
  @param {string} profileDir Path to the profile directory to install into.
  @return {!promise.Promise.<string>} The LD_LIBRARY_PATH prefix string to use
  for the installed libs.