AU: Use crossystem hwid to obtain the hardware class.

This is more portable than reading the HWID from the ACPI file and should work
on ARM.

BUG=chromium-os:15255
TEST=unit tests, ran AU on Cr-48, checked the Omaha update check request

Change-Id: I8a2750140da7da99c217a6976f46b1b226696276
Reviewed-on: http://gerrit.chromium.org/gerrit/1078
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
diff --git a/utils.h b/utils.h
index fb30055..7b39cd4 100644
--- a/utils.h
+++ b/utils.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -33,6 +33,9 @@
 // boot mode. Returns false if the boot mode is developer.
 bool IsNormalBootMode();
 
+// Returns the HWID or an empty string on error.
+std::string GetHardwareClass();
+
 // 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);