Add en/update_firmware_slow_extra_warning.txt firmware update message.

BUG=b:112485400
TEST=Built new image containing this change, dependencies, and a
TCON firmware updater which uses this message.  Booted from the image on
a DUT with old TCON firmware.  This new message was displayed as the
TCON firmware was updated.

Change-Id: I36f3e60806ac54ce74994192b132c1f8b0059581
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/assets/+/1983330
Tested-by: Matthew Blecker <matthewb@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Commit-Queue: Matthew Blecker <matthewb@chromium.org>
diff --git a/text/boot_messages/cros_bootmsg.grd b/text/boot_messages/cros_bootmsg.grd
index 05b2189..8df963f 100644
--- a/text/boot_messages/cros_bootmsg.grd
+++ b/text/boot_messages/cros_bootmsg.grd
@@ -70,6 +70,8 @@
         file="en/block_devmode_virtual.txt" />
       <structure type="txt" name="UPDATE_DETACHABLE_BASE_FIRMWARE"
         file="en/update_detachable_base_firmware.txt" />
+      <structure type="txt" name="UPDATE_FIRMWARE_SLOW_EXTRA_WARNING"
+        file="en/update_firmware_slow_extra_warning.txt" />
       <structure type="txt" name="UPDATE_TOUCHPAD_FIRMWARE"
         file="en/update_touchpad_firmware.txt" />
       <structure type="txt" name="UPDATE_TOUCHSCREEN_FIRMWARE"
diff --git a/text/boot_messages/en/update_firmware_slow_extra_warning.txt b/text/boot_messages/en/update_firmware_slow_extra_warning.txt
new file mode 100644
index 0000000..a9fab0b
--- /dev/null
+++ b/text/boot_messages/en/update_firmware_slow_extra_warning.txt
@@ -0,0 +1,5 @@
+Your system is applying an important update.
+
+Do not shutdown or reboot.
+
+This may take several minutes.
diff --git a/text/display_boot_message b/text/display_boot_message
index 8a634fe..0e85b27 100755
--- a/text/display_boot_message
+++ b/text/display_boot_message
@@ -95,7 +95,8 @@
   case "${message}" in
     enter_dev2 | leave_dev | self_repair | update_firmware | power_wash | \
         show_spinner | wipe | update_detachable_base_firmware | \
-        update_touchpad_firmware | update_touchscreen_firmware)
+        update_touchpad_firmware | update_touchscreen_firmware | \
+        update_firmware_slow_extra_warning)
       return 0
       ;;
     *)