factory_shim: Change the size of ram disk

The 400M ram disk is not enough when installing. This CL should be a
temporary solution.

BUG=b:122348657, b:129663373
TEST=Manually test on my local device

Change-Id: I457ffb35de767267fc7398bd0b94239730913a88
Reviewed-on: https://chromium-review.googlesource.com/1404612
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Chun-Tsen Kuo <chuntsen@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
diff --git a/factory_shim/bootstrap.sh b/factory_shim/bootstrap.sh
index a81b2d4..dc69a57 100755
--- a/factory_shim/bootstrap.sh
+++ b/factory_shim/bootstrap.sh
@@ -23,7 +23,7 @@
 LOG_FILE=${LOG_DIR}/factory_initramfs.log
 
 # Size of the root ramdisk.
-TMPFS_SIZE=400M
+TMPFS_SIZE=512M
 
 # Special file systems required in addition to the root file system.
 BASE_MOUNTS="/sys /proc /dev"