AU: Really delta compress the kernel if an old kernel is provided.

generate_delta_main.cc

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>
 
@@ skipping 84 matching lines @@
     LOG(INFO) << "done applying delta.";
     return 0;
   }
   CHECK(!FLAGS_new_image.empty());
   CHECK(!FLAGS_out_file.empty());
   CHECK(!FLAGS_new_kernel.empty());
   if (FLAGS_old_image.empty()) {
     LOG(INFO) << "Generating full update";
   } else {
     LOG(INFO) << "Generating delta update";
-    CHECK(!FLAGS_old_kernel.empty());
     CHECK(!FLAGS_old_dir.empty());
     CHECK(!FLAGS_new_dir.empty());
     if ((!IsDir(FLAGS_old_dir.c_str())) || (!IsDir(FLAGS_new_dir.c_str()))) {
       LOG(FATAL) << "old_dir or new_dir not directory";
     }
   }
   DeltaDiffGenerator::GenerateDeltaUpdateFile(FLAGS_old_dir,
                                               FLAGS_old_image,
                                               FLAGS_new_dir,
                                               FLAGS_new_image,
                                               FLAGS_old_kernel,
                                               FLAGS_new_kernel,
                                               FLAGS_out_file,
                                               FLAGS_private_key);
 
   return 0;
 }
 
 }  // namespace {}
 
 }  // namespace chromeos_update_engine
 
 int main(int argc, char** argv) {
   return chromeos_update_engine::Main(argc, argv);
 }