Use dpkg --add-architecture if it's available.

build/install-chroot.sh

 #!/bin/bash -e
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script installs Debian-derived distributions in a chroot environment.
 # It can for example be used to have an accurate 32bit build and test
 # environment when otherwise working on a 64bit machine.
 # N. B. it is unlikely that this script will ever work on anything other than a
@@ skipping 569 matching lines @@
   [ -r /etc/locale.gen ] &&
     sed -i "s/^# \($l\)/\1/" /etc/locale.gen
   locale-gen $LANG en_US en_US.UTF-8' || :
 
 # Enable multi-arch support, if available
 sudo "/usr/local/bin/${target%bit}" dpkg --assert-multi-arch >&/dev/null &&
   [ -r "/var/lib/chroot/${target}/etc/apt/sources.list" ] && {
   sudo sed -i 's/ / [arch=amd64,i386] /' \
               "/var/lib/chroot/${target}/etc/apt/sources.list"
   [ -d /var/lib/chroot/${target}/etc/dpkg/dpkg.cfg.d/ ] &&
-  echo foreign-architecture \
-       $([ "${arch}" = "32bit" ] && echo amd64 || echo i386) |
-    sudo sh -c "cat >'/var/lib/chroot/${target}/etc/dpkg/dpkg.cfg.d/multiarch'"
+  sudo "/usr/local/bin/${target%bit}" dpkg --add-architecture \
+      $([ "${arch}" = "32bit" ] && echo amd64 || echo i386) >&/dev/null ||
+    echo foreign-architecture \
+        $([ "${arch}" = "32bit" ] && echo amd64 || echo i386) |
+      sudo sh -c \
+        "cat >'/var/lib/chroot/${target}/etc/dpkg/dpkg.cfg.d/multiarch'"
 }
 
 # Configure "sudo" package
 sudo "/usr/local/bin/${target%bit}" /bin/sh -c '
   egrep -qs '"'^$(id -nu) '"' /etc/sudoers ||
   echo '"'$(id -nu) ALL=(ALL) ALL'"' >>/etc/sudoers'
 
 # Install a few more commonly used packages
 sudo "/usr/local/bin/${target%bit}" apt-get -y install                         \
   autoconf automake1.9 dpkg-dev g++-multilib gcc-multilib gdb less libtool     \
@@ skipping 201 matching lines @@
 
 For Chrome, this probably means you want to make your "out" directory a
 symbolic link that points somewhere inside of "${HOME}/chroot".
 
 You still need to run "gclient runhooks" whenever you switch from building
 outside of the chroot to inside of the chroot. But you will find that you
 don't have to repeatedly erase and then completely rebuild all your object
 and binary files.
 
 EOF