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

base/process/process_posix.cc

Index: base/process/process_posix.cc
diff --git a/base/process/process_posix.cc b/base/process/process_posix.cc
index a7d16f87304f2b38953c9ca9fe42f47e6c0c7634..bb987d0bbb7d453039a0445659d6d405a03032df 100644
--- a/base/process/process_posix.cc
+++ b/base/process/process_posix.cc
@@ -193,11 +193,13 @@ bool WaitForExitWithTimeoutImpl(base::ProcessHandle handle,
   if (!WaitpidWithTimeout(handle, &status, timeout))
     return false;
   if (WIFSIGNALED(status)) {
-    *exit_code = -1;
+    if (exit_code)
+      *exit_code = -1;
     return true;
   }
   if (WIFEXITED(status)) {
-    *exit_code = WEXITSTATUS(status);
+    if (exit_code)
+      *exit_code = WEXITSTATUS(status);
     return true;
   }
   return false;