Rewrite base::Bind into base::BindOnce on trivial cases in base

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 9746e35ea70ac880f564db0adc20139c4ab14f63..ce05081244aa48c15d1e2de0d16a1b3fd0abfb1f 100644
--- a/base/files/file_descriptor_watcher_posix.cc
+++ b/base/files/file_descriptor_watcher_posix.cc
@@ -124,8 +124,8 @@ void FileDescriptorWatcher::Controller::Watcher::OnFileCanReadWithoutBlocking(
   DCHECK(thread_checker_.CalledOnValidThread());
 
   // Run the callback on the sequence on which the watch was initiated.
-  callback_task_runner_->PostTask(FROM_HERE,
-                                  Bind(&Controller::RunCallback, controller_));
+  callback_task_runner_->PostTask(
+      FROM_HERE, BindOnce(&Controller::RunCallback, controller_));
 }
 
 void FileDescriptorWatcher::Controller::Watcher::OnFileCanWriteWithoutBlocking(
@@ -135,8 +135,8 @@ void FileDescriptorWatcher::Controller::Watcher::OnFileCanWriteWithoutBlocking(
   DCHECK(thread_checker_.CalledOnValidThread());
 
   // Run the callback on the sequence on which the watch was initiated.
-  callback_task_runner_->PostTask(FROM_HERE,
-                                  Bind(&Controller::RunCallback, controller_));
+  callback_task_runner_->PostTask(
+      FROM_HERE, BindOnce(&Controller::RunCallback, controller_));
 }
 
 void FileDescriptorWatcher::Controller::Watcher::
@@ -170,7 +170,7 @@ void FileDescriptorWatcher::Controller::StartWatching() {
   // Controller's destructor. Since this delete task hasn't been posted yet, it
   // can't run before the task posted below.
   message_loop_for_io_task_runner_->PostTask(
-      FROM_HERE, Bind(&Watcher::StartWatching, Unretained(watcher_.get())));
+      FROM_HERE, BindOnce(&Watcher::StartWatching, Unretained(watcher_.get())));
 }
 
 void FileDescriptorWatcher::Controller::RunCallback() {