AU: when compiling locally, use cros-debug for libchrome

BUG=6797
TEST=compiled locally. saw this fix the error

Review URL: http://codereview.chromium.org/3386007
diff --git a/setup_dev_packages b/setup_dev_packages
index 5c4accb..4709d11 100755
--- a/setup_dev_packages
+++ b/setup_dev_packages
@@ -6,7 +6,7 @@
 
 set -ex
 
-sudo USE=-crash emerge -DNauv1 \
+sudo USE="-crash cros-debug" emerge -DNauv1 \
   chromeos-base/libchrome \
   chromeos-base/metrics \
   dev-cpp/gmock \