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

chrome/app/chrome_watcher_client_unittest_win.cc

Index: chrome/app/chrome_watcher_client_unittest_win.cc
diff --git a/chrome/app/chrome_watcher_client_unittest_win.cc b/chrome/app/chrome_watcher_client_unittest_win.cc
index 5b916138d14ea2f46a2cdc12a968c138f0005cd3..cb09fab2e9f08a763eb0f3c4bc98bdd95e91acae 100644
--- a/chrome/app/chrome_watcher_client_unittest_win.cc
+++ b/chrome/app/chrome_watcher_client_unittest_win.cc
@@ -221,8 +221,7 @@ class ChromeWatcherClientTest : public testing::Test {
   void TearDown() override {
     // Even if we never launched, the following is harmless.
     SignalExit();
-    int exit_code = 0;
-    thread_.client().WaitForExit(&exit_code);
+    thread_.client().WaitForExit(NULL);
     thread_.Join();
   }