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

chrome/installer/setup/run_all_unittests.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 "base/command_line.h"
 #include "base/test/test_suite.h"
 #include "chrome/common/chrome_paths.h"
+#include "chrome/installer/setup/setup_util_unittest.h"
 
 int main(int argc, char** argv) {
   TestSuite test_suite(argc, argv);
 
+  // Handle the --adjust-process-priority switch, which is used to test the
+  // installer::AdjustProcessPriority() function in a subprocess.
+  if (CommandLine::ForCurrentProcess()->HasSwitch(kAdjustProcessPriority))
+    return DoProcessPriorityAdjustment();
+
   // Register Chrome Path provider so that we can get test data dir.
   chrome::RegisterPathProvider();
 
   return test_suite.Run();
 }