Modify postinstall to avoid x86-specific dependencies.

chromeos-postinst

Index: chromeos-postinst
diff --git a/chromeos-postinst b/chromeos-postinst
index e183247ab9c24ba9f46ed953b704212d00987534..6504e4e17f7acfade27ab1fd8b367c72d388c5ed 100755
--- a/chromeos-postinst
+++ b/chromeos-postinst
@@ -14,7 +14,7 @@ INSTALL_ROOT=`dirname "$0"`
 INSTALL_DEV="$1"
 POSTCOMMIT="$2"
 # Find whole disk device.
-ROOT_DEV=${INSTALL_DEV%%[0-9]*}
+ROOT_DEV=$(get_block_dev_from_partition_dev ${INSTALL_DEV})
 NEW_PART_NUM=${INSTALL_DEV##*/*[a-z]}
 
 case ${NEW_PART_NUM} in
@@ -39,17 +39,20 @@ if [ "$POSTCOMMIT" != "--postcommit" ]; then
   echo " Set boot target to ${INSTALL_DEV}: \
 Partition ${NEW_PART_NUM}, Slot ${BOOT_SLOT}"
 
-  echo "Updating /boot/extlinux.conf target"
-  # If the mount-point is read-write, update the bootloader
-  # Only update extlinux.conf if $1 is non-empty
-  if [ -n "$INSTALL_DEV" ]; then
-    # Set default label to chromeos-hd.
-    sed -i 's/^DEFAULT .*/DEFAULT chromeos-hd/' \
-        "$INSTALL_ROOT"/boot/extlinux.conf || true
-    sed -i "{ s:HDROOT:$INSTALL_DEV: }" \
-        "$INSTALL_ROOT"/boot/extlinux.conf || true
+  if [ -f /boot/extlinux.conf ]; then
+    echo "Updating /boot/extlinux.conf target"
+    # If the mount-point is read-write, update the bootloader
+    # Only update extlinux.conf if $1 is non-empty
+    if [ -n "$INSTALL_DEV" ]; then
+      # Set default label to chromeos-hd.
+      sed -i 's/^DEFAULT .*/DEFAULT chromeos-hd/' \
+          "$INSTALL_ROOT"/boot/extlinux.conf || true
+      sed -i "{ s:HDROOT:$INSTALL_DEV: }" \
+          "$INSTALL_ROOT"/boot/extlinux.conf || true
+    fi
   fi
 
+
   echo "Updating grub target for EFI BIOS"
   # Set up grub.cfg
   ${INSTALL_ROOT}/usr/sbin/chromeos-setimage ${BOOT_SLOT} \
@@ -60,6 +63,7 @@ Partition ${NEW_PART_NUM}, Slot ${BOOT_SLOT}"
   sync
   echo 3 > /proc/sys/vm/drop_caches
 
+
   echo "Updating gpt PMBR target for legacy BIOS"
   # Configure the PMBR to boot the new image.
   #