Mac: ensure child processes are properly reaped -- eliminate Helper zombies.

chrome/common/process_watcher_mac.cc

Index: chrome/common/process_watcher_mac.cc
diff --git a/chrome/common/process_watcher_mac.cc b/chrome/common/process_watcher_mac.cc
index 2d5d185dc55bba513ccdafa3bb091e0024d349ca..be5b9f7337532fe63e20994247879cb9a8fb608d 100644
--- a/chrome/common/process_watcher_mac.cc
+++ b/chrome/common/process_watcher_mac.cc
@@ -42,7 +42,9 @@ void WaitForChildToDie(pid_t child, unsigned timeout) {
   int result = HANDLE_EINTR(kevent(kq, &event_to_add, 1, NULL, 0, NULL));
   if (result == -1 && errno == ESRCH) {
     // A "No Such Process" error is fine, the process may have died already
-    // and been reaped by someone else.
+    // and been reaped by someone else. But make sure that it was/is reaped.
+    // Don't report an error in case it was already reaped.
+    HANDLE_EINTR(waitpid(child, NULL, WNOHANG));
     return;
   }