enter_chroot: Mount binfmt_misc when entering chroot

The binfmt handler is used for running ARM unit tests under qemu.

BUG=chromium:318497
TEST=cat /proc/sys/fs/binfmt_misc/status shows registered handlers
     after entering chroot.

Change-Id: I2a0b087df4ba35c6793043237d708b6a39925163
Reviewed-on: https://chromium-review.googlesource.com/178686
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Queue: Gaurav Shah <gauravsh@chromium.org>
Tested-by: Gaurav Shah <gauravsh@chromium.org>
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index cbd5a1a..08cfafe 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -243,6 +243,9 @@
     MOUNT_CACHE=$(echo $(awk '{print $2}' /proc/mounts))
     setup_mount none "-t proc" /proc
     setup_mount none "-t sysfs" /sys
+    if grep -q binfmt_misc /proc/filesystems; then
+      setup_mount binfmt_misc "-t binfmt_misc" /proc/sys/fs/binfmt_misc
+    fi
     setup_mount /dev "--bind" /dev
     setup_mount /dev/pts "--bind" /dev/pts
     if [[ -d /run ]]; then