vboot_reference: Don't use session_manager_use_flags.txt.

Make ensure_no_nonrelease_files.sh stop grepping
/etc/session_manager_use_flags.txt for USE flags. Instead,
look for non-comment lines in /etc/chrome_dev.conf.

BUG=chromium:377301
TEST=manual: ran against images both with and without
     extra config directives
BRANCH=none
CQ-DEPEND=I86d01f4a551433527bb434dc62c30fb44082f774
CQ-DEPEND=Ic030207840b6be79b51486d1706573241a01c08d

Change-Id: Iefeefd936dc7706ed74340edb6521621885bbe25
Reviewed-on: https://chromium-review.googlesource.com/203463
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Daniel Erat <derat@chromium.org>
Tested-by: Daniel Erat <derat@chromium.org>

scripts/image_signing/ensure_no_nonrelease_files.sh

@@ -48,17 +48,15 @@ main() {
         fi
     done
 
-    # Some things which used to be flag-files, checked-for by this
-    # test, are now tracked as use-flags.
-    local useflag_path="$rootfs/etc/session_manager_use_flags.txt"
-    for prefix in dangerous_ test_; do
-        local matches=$(grep "^$prefix" "$useflag_path")
-        if [ -n "$matches" ]; then
-            echo "FAIL: Found non-release use flags in $useflag_path:"
-            echo "$matches"
-            testfail=1
-        fi
-    done
+    # Verify that session_manager isn't configured to pass additional
+    # environment variables or command-line arguments to Chrome.
+    local config_path="$rootfs/etc/chrome_dev.conf"
+    local matches=$(grep "^[^#]" "${config_path}")
+    if [ -n "$matches" ]; then
+        echo "FAIL: Found commands in $config_path:"
+        echo "$matches"
+        testfail=1
+    fi
 
     exit $testfail
 }