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

components/browser_watcher/exit_code_watcher_win_unittest.cc

Index: components/browser_watcher/exit_code_watcher_win_unittest.cc
diff --git a/components/browser_watcher/exit_code_watcher_win_unittest.cc b/components/browser_watcher/exit_code_watcher_win_unittest.cc
index e89301bfe8f26098915b7adf4923b5132ab9a50b..c8642113b806f6abdca0f2cf78d4342bcb8f0d82 100644
--- a/components/browser_watcher/exit_code_watcher_win_unittest.cc
+++ b/components/browser_watcher/exit_code_watcher_win_unittest.cc
@@ -39,8 +39,7 @@ class ScopedSleeperProcess {
   ~ScopedSleeperProcess() {
     if (process_.IsValid()) {
       process_.Terminate(-1, false);
-      int exit_code = 0;
-      EXPECT_TRUE(process_.WaitForExit(&exit_code));
+      EXPECT_TRUE(process_.WaitForExit(NULL));
     }
   }