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

chrome/installer/setup/run_all_unittests.cc

Index: chrome/installer/setup/run_all_unittests.cc
diff --git a/chrome/installer/setup/run_all_unittests.cc b/chrome/installer/setup/run_all_unittests.cc
index 1f55d012ee73ab1a5d6dbd4a33a713482f8c5489..a309b110884d6b9b074c427d76d882187803e28c 100644
--- a/chrome/installer/setup/run_all_unittests.cc
+++ b/chrome/installer/setup/run_all_unittests.cc
@@ -2,12 +2,19 @@
 // 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();