AU: Use Omaha ID rather than MAC address in delta updater

src/platform/update_engine/utils.cc

 // Copyright (c) 2009 The Chromium 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 "update_engine/utils.h"
 #include <sys/mount.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <algorithm>
 #include "chromeos/obsolete_logging.h"
+#include "update_engine/file_writer.h"
 
 using std::min;
 using std::string;
 using std::vector;
 
 namespace chromeos_update_engine {
 
 namespace utils {
 
+bool WriteFile(const char* path, const char* data, int data_len) {
+  DirectFileWriter writer;
+  TEST_AND_RETURN_FALSE_ERRNO(0 == writer.Open(path,
+                                               O_WRONLY | O_CREAT | O_TRUNC,
+                                               0666));
+  ScopedFileWriterCloser closer(&writer);
+  TEST_AND_RETURN_FALSE_ERRNO(data_len == writer.Write(data, data_len));
+  return true;
+}
+
 bool ReadFile(const std::string& path, std::vector<char>* out) {
   CHECK(out);
   FILE* fp = fopen(path.c_str(), "r");
   if (!fp)
     return false;
   const size_t kChunkSize = 1024;
   size_t read_size;
   do {
     char buf[kChunkSize];
     read_size = fread(buf, 1, kChunkSize, fp);
@@ skipping 208 matching lines @@
   TEST_AND_RETURN_FALSE_ERRNO(umount(mountpoint.c_str()) == 0);
   return true;
 }
 
 const string kStatefulPartition = "/mnt/stateful_partition";
 
 }  // namespace utils
 
 }  // namespace chromeos_update_engine