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

base/files/file_descriptor_watcher_posix.cc

Index: base/files/file_descriptor_watcher_posix.cc
diff --git a/base/files/file_descriptor_watcher_posix.cc b/base/files/file_descriptor_watcher_posix.cc
index 49ac5d43a4a6080fbb18e0d63138c2480232b0dc..9746e35ea70ac880f564db0adc20139c4ab14f63 100644
--- a/base/files/file_descriptor_watcher_posix.cc
+++ b/base/files/file_descriptor_watcher_posix.cc
@@ -92,7 +92,10 @@ FileDescriptorWatcher::Controller::Watcher::Watcher(
     WeakPtr<Controller> controller,
     MessageLoopForIO::Mode mode,
     int fd)
-    : controller_(controller), mode_(mode), fd_(fd) {
+    : file_descriptor_watcher_(FROM_HERE),
+      controller_(controller),
+      mode_(mode),
+      fd_(fd) {
   DCHECK(callback_task_runner_);
   thread_checker_.DetachFromThread();
 }