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

src/platform/update_engine/utils.h

 // 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.
 
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__
 
 #include <set>
 #include <string>
 #include <vector>
 #include "update_engine/action.h"
 #include "update_engine/action_processor.h"
 
 namespace chromeos_update_engine {
 
 namespace utils {
 
+// Writes the data passed to path. The file at path will be overwritten if it
+// exists. Returns true on success, false otherwise.
+bool WriteFile(const char* path, const char* data, int data_len);
+
 // Returns the entire contents of the file at path. Returns true on success.
 bool ReadFile(const std::string& path, std::vector<char>* out);
 bool ReadFileToString(const std::string& path, std::string* out);
 
 std::string ErrnoNumberAsString(int err);
 
 // Strips duplicate slashes, and optionally removes all trailing slashes.
 // Does not compact /./ or /../.
 std::string NormalizePath(const std::string& path, bool strip_trailing_slash);
 
@@ skipping 147 matching lines @@
     bool _success = (_x);                                                      \
     if (!_success) {                                                           \
       LOG(ERROR) << #_x " failed.";                                            \
       return;                                                                  \
     }                                                                          \
   } while (0)
 
 
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__