AU: Include a bit flag (bit 31) in error codes to indicate non-normal boot mode.

BUG=chromium-os:10320
TEST=unit test, tested on device in normal and dev mode

Change-Id: I67d695bc167a4cc1a638711f047e2b86f8eaa8f1

Review URL: http://codereview.chromium.org/6098008
diff --git a/setup_dev_packages b/setup_dev_packages
index d5ddcc7..8a9182c 100755
--- a/setup_dev_packages
+++ b/setup_dev_packages
@@ -7,6 +7,7 @@
 set -ex
 
 sudo USE="-crash cros-debug" emerge -DNauv1 \
+  chromeos-base/cros_boot_mode \
   chromeos-base/hard-host-depends \
   chromeos-base/libchrome \
   chromeos-base/metrics \