Use crossystem rather than cros_boot_mode.

Also, make the check for normal mode a bit more restrictive.

BUG=chromium-os:13283
TEST=unit tests, tested on device

Change-Id: I3ec8a4c5526208d6f050ec2e152604b2ead76f27

Review URL: http://codereview.chromium.org/6719012
diff --git a/utils.h b/utils.h
index a17f241..fb30055 100644
--- a/utils.h
+++ b/utils.h
@@ -29,8 +29,8 @@
 // otherwise.
 bool IsOOBEComplete();
 
-// Returns true if the boot mode is normal, false otherwise (e.g., developer or
-// recovery).
+// Returns true if the boot mode is normal or if it's unable to determine the
+// boot mode. Returns false if the boot mode is developer.
 bool IsNormalBootMode();
 
 // Writes the data passed to path. The file at path will be overwritten if it