Add upgrade script to move incremental chrome build content.

Via distfiles bind mounting, chrome build output was being cached
across chroot replacements.  This potentially is desirable, but
wasn't explicitly planned for and violates an assumption of the
canaries.

As such move the content to it's new location.

BUG=None
TEST=emerge-<board> chromeos-chrome
CQ-DEPEND=Ibfc5d42e74861ff498dd2cb6cc2d7be6ec0ded60

Change-Id: I18e384f0fc1cedb3c70ab85178103765322370eb
Reviewed-on: https://gerrit.chromium.org/gerrit/15383
Reviewed-by: David James <davidjames@chromium.org>
Tested-by: Brian Harring <ferringb@chromium.org>
diff --git a/sdk_lib/make_chroot.sh b/sdk_lib/make_chroot.sh
index 2ac5767..5479a0f 100755
--- a/sdk_lib/make_chroot.sh
+++ b/sdk_lib/make_chroot.sh
@@ -198,7 +198,13 @@
    sudo chmod 0644 "${FLAGS_chroot}"/etc/make.conf.user
 
    # Create directories referred to by our conf files.
-   sudo mkdir -p -m 775 "${FLAGS_chroot}/var/lib/portage/pkgs"
+   sudo mkdir -p -m 775 "${FLAGS_chroot}/var/lib/portage/pkgs" \
+     "${FLAGS_chroot}/var/cache/distfiles" \
+     "${FLAGS_chroot}/var/cache/chromeos-chrome"
+
+   # Run this from w/in the chroot so we use whatever uid/gid
+   # these are defined as w/in the chroot.
+   sudo_chroot chown "${USER}:portage" /var/cache/chromeos-chrome
 
    # These are created for compatibility while transitioning
    # make.conf and friends over to the new location.