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

base/process/process.h

Index: base/process/process.h
diff --git a/base/process/process.h b/base/process/process.h
index 808baeb1fc6ebdf7a9603b7b9b8d070b37694cdd..50dfef1c4109e22cef4c9dabe1f4913cd7e00483 100644
--- a/base/process/process.h
+++ b/base/process/process.h
@@ -102,9 +102,13 @@ class BASE_EXPORT Process {
   // On POSIX, if the process has been signaled then |exit_code| is set to -1.
   // On Linux this must be a child process, however on Mac and Windows it can be
   // any process.
+  // NOTE: |exit_code| is optional, nullptr can be passed if the exit code is
+  // not required.
   bool WaitForExit(int* exit_code);
 
   // Same as WaitForExit() but only waits for up to |timeout|.
+  // NOTE: |exit_code| is optional, nullptr can be passed if the exit code
+  // is not required.
   bool WaitForExitWithTimeout(TimeDelta timeout, int* exit_code);
 
   // A process is backgrounded when it's priority is lower than normal.