update_payload: Regenerate protobuf to include IMGDIFF.

Generated from update_metadata.proto using protoc 2.5.0

BUG=b:26456666
TEST=./checker_unittest.py

Change-Id: I9dc7db00be8afb2f78e80bec910f9ca83a55a9a1
Reviewed-on: https://chromium-review.googlesource.com/329237
Commit-Ready: Sen Jiang <senj@chromium.org>
Tested-by: Sen Jiang <senj@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
diff --git a/scripts/update_payload/checker_unittest.py b/scripts/update_payload/checker_unittest.py
index d7c6025..b05c728 100755
--- a/scripts/update_payload/checker_unittest.py
+++ b/scripts/update_payload/checker_unittest.py
@@ -38,6 +38,7 @@
       'ZERO': common.OpType.ZERO,
       'DISCARD': common.OpType.DISCARD,
       'REPLACE_XZ': common.OpType.REPLACE_XZ,
+      'IMGDIFF': common.OpType.IMGDIFF,
   }
   return op_name_to_type[op_name]