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

chrome/common/process_watcher_mac.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/common/process_watcher.h"
 
 #include <errno.h>
 #include <signal.h>
 #include <sys/event.h>
 #include <sys/types.h>
@@ skipping 24 matching lines @@
     PLOG(ERROR) << "Failed to create kqueue";
     return;
   }
 
   struct kevent event_to_add = {0};
   EV_SET(&event_to_add, child, EVFILT_PROC, EV_ADD, NOTE_EXIT, 0, NULL);
   // Register interest with kqueue.
   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;
   }
 
   if (result == -1) {
     PLOG(ERROR) << "Failed to register event to listen for death of pid "
                 << child;
     return;
   }
 
   struct kevent event = {0};
@@ skipping 53 matching lines @@
     PLOG(ERROR) << "While waiting for " << child << " to terminate we"
                << " failed to deliver a SIGKILL signal";
   }
 }
 
 }  // namespace
 
 void ProcessWatcher::EnsureProcessTerminated(base::ProcessHandle process) {
   WaitForChildToDie(process, 2);
 }