Lower the I/O priority of the installer when resonable.

chrome/installer/setup/setup_util_unittest.h

+// Copyright 2013 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 CHROME_INSTALLER_SETUP_SETUP_UTIL_UNITTEST_H_
+#define CHROME_INSTALLER_SETUP_SETUP_UTIL_UNITTEST_H_
+
+// A command line switch that causes the test harness to exit with the result of
+// DoProcessPriorityAdjustment rather than executing all tests.
+extern const char kAdjustProcessPriority[];
+
+// Process exit codes when the test harness is run with the
+// kAdjustProcessPriority switch.
+enum PriorityClassChangeResult {
+  PCCR_UNKNOWN,
+  PCCR_UNCHANGED,
+  PCCR_CHANGED,
+};
+
+// Calls AdjustProcessPriority() and returns PCCR_CHANGED or PCCR_UNCHANGED
+// based on its true or false result (respectively).
+PriorityClassChangeResult DoProcessPriorityAdjustment();
+
+#endif  // CHROME_INSTALLER_SETUP_SETUP_UTIL_UNITTEST_H_