Use the location where FileDescriptorWatcher is created to track the libevent handlers

base/message_loop/message_pump_io_ios.cc

 // Copyright 2012 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 "base/message_loop/message_pump_io_ios.h"
 
 namespace base {
 
-MessagePumpIOSForIO::FileDescriptorWatcher::FileDescriptorWatcher()
+MessagePumpIOSForIO::FileDescriptorWatcher::FileDescriptorWatcher(
+    const tracked_objects::Location& from_here)
     : is_persistent_(false),
       fdref_(NULL),
       callback_types_(0),
       fd_source_(NULL),
-      watcher_(NULL) {
-}
+      watcher_(NULL),
+      created_from_location_(from_here) {}
 
 MessagePumpIOSForIO::FileDescriptorWatcher::~FileDescriptorWatcher() {
   StopWatchingFileDescriptor();
 }
 
 bool MessagePumpIOSForIO::FileDescriptorWatcher::StopWatchingFileDescriptor() {
   if (fdref_ == NULL)
     return true;
 
   CFFileDescriptorDisableCallBacks(fdref_.get(), callback_types_);
@@ skipping 154 matching lines @@
 
   // Re-enable callbacks after the read/write if the file descriptor is still
   // valid and the controller is persistent.
   if (CFFileDescriptorIsValid(fdref) && controller->is_persistent_) {
     DCHECK_EQ(fdref, controller->fdref_.get());
     CFFileDescriptorEnableCallBacks(fdref, callback_types);
   }
 }
 
 }  // namespace base