Handled nullptr argument in WaitForExit() and WaitForExitWithTimeout() methods.

ash/test/test_metro_viewer_process_host.cc

Index: ash/test/test_metro_viewer_process_host.cc
diff --git a/ash/test/test_metro_viewer_process_host.cc b/ash/test/test_metro_viewer_process_host.cc
index c680e456a790c0c2f898d89286c84d8a6a971ab0..8527e19dda2920466e54cc762e63f4d8c5bc7c46 100644
--- a/ash/test/test_metro_viewer_process_host.cc
+++ b/ash/test/test_metro_viewer_process_host.cc
@@ -30,8 +30,7 @@ void TestMetroViewerProcessHost::TerminateViewer() {
         PROCESS_QUERY_INFORMATION | SYNCHRONIZE | PROCESS_TERMINATE);
     if (viewer_process.IsValid()) {
       viewer_process.Terminate(0, false);
-      int exit_code;
-      viewer_process.WaitForExit(&exit_code);
+      viewer_process.WaitForExit(nullptr);
     }
   }
 }