Make ProcessWatcher use kqueues on Mac.

chrome/common/process_watcher.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef CHROME_COMMON_PROCESS_WATCHER_H_
 #define CHROME_COMMON_PROCESS_WATCHER_H_
 
 #include "build/build_config.h"
 
 #include "base/basictypes.h"
 #include "base/process_util.h"
 
 class ProcessWatcher {
  public:
   // This method ensures that the specified process eventually terminates, and
   // then it closes the given process handle.
   //
   // It assumes that the process has already been signalled to exit, and it
   // begins by waiting a small amount of time for it to exit.  If the process
   // does not appear to have exited, then this function starts to become
   // aggressive about ensuring that the process terminates.
   //
-  // This method does not block the calling thread.
+  // On Linux this method does not block the calling thread.
+  // On OS X this method may block for up to 2 seconds.
   //
   // NOTE: The process handle must have been opened with the PROCESS_TERMINATE
   // and SYNCHRONIZE permissions.
   //
   static void EnsureProcessTerminated(base::ProcessHandle process_handle);
 
-#if defined(OS_POSIX)
+#if defined(OS_LINUX)
   // The nicer version of EnsureProcessTerminated() that is patient and will
   // wait for |process_handle| to finish and then reap it.
   static void EnsureProcessGetsReaped(base::ProcessHandle process_handle);
 #endif
 
  private:
   // Do not instantiate this class.
   ProcessWatcher();
 
   DISALLOW_COPY_AND_ASSIGN(ProcessWatcher);
 };
 
 #endif  // CHROME_COMMON_PROCESS_WATCHER_H_