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

src/platform/update_engine/utils.cc

Index: src/platform/update_engine/utils.cc
diff --git a/src/platform/update_engine/utils.cc b/src/platform/update_engine/utils.cc
index 693062df6a4a77aa3ed2b1b88640a6fbaf89feee..9fa0906c0eec4d5a3244cf78ba8ae0eb5913fe23 100644
--- a/src/platform/update_engine/utils.cc
+++ b/src/platform/update_engine/utils.cc
@@ -8,12 +8,14 @@
 #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;
@@ -23,6 +25,16 @@ 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");