Revert of file_manager: Migrate FILE thread to TaskScheduler

chrome/browser/chromeos/file_manager/file_watcher.cc

Index: chrome/browser/chromeos/file_manager/file_watcher.cc
diff --git a/chrome/browser/chromeos/file_manager/file_watcher.cc b/chrome/browser/chromeos/file_manager/file_watcher.cc
index 60f9a6e21913c0aba66abfa2659f45bd54b155fd..e169e9682fe14c0eadac7e665e6b507aec72525a 100644
--- a/chrome/browser/chromeos/file_manager/file_watcher.cc
+++ b/chrome/browser/chromeos/file_manager/file_watcher.cc
@@ -5,8 +5,6 @@
 #include "chrome/browser/chromeos/file_manager/file_watcher.h"
 
 #include "base/bind.h"
-#include "base/task_runner_util.h"
-#include "base/task_scheduler/post_task.h"
 #include "content/public/browser/browser_thread.h"
 #include "google_apis/drive/task_util.h"
 
@@ -20,6 +18,7 @@
 base::FilePathWatcher* CreateAndStartFilePathWatcher(
     const base::FilePath& watch_path,
     const base::FilePathWatcher::Callback& callback) {
+  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
   DCHECK(!callback.is_null());
 
   std::unique_ptr<base::FilePathWatcher> watcher(new base::FilePathWatcher);
@@ -32,9 +31,7 @@
 }  // namespace
 
 FileWatcher::FileWatcher(const base::FilePath& virtual_path)
-    : sequenced_task_runner_(base::CreateSequencedTaskRunnerWithTraits(
-          {base::MayBlock(), base::TaskPriority::USER_VISIBLE})),
-      local_file_watcher_(NULL),
+    : local_file_watcher_(NULL),
       virtual_path_(virtual_path),
       weak_ptr_factory_(this) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
@@ -43,7 +40,9 @@
 FileWatcher::~FileWatcher() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  sequenced_task_runner_->DeleteSoon(FROM_HERE, local_file_watcher_);
+  BrowserThread::DeleteSoon(BrowserThread::FILE,
+                            FROM_HERE,
+                            local_file_watcher_);
 }
 
 void FileWatcher::AddExtension(const std::string& extension_id) {
@@ -87,11 +86,14 @@
   DCHECK(!callback.is_null());
   DCHECK(!local_file_watcher_);
 
-  base::PostTaskAndReplyWithResult(
-      sequenced_task_runner_.get(), FROM_HERE,
-      base::Bind(&CreateAndStartFilePathWatcher, local_path,
+  BrowserThread::PostTaskAndReplyWithResult(
+      BrowserThread::FILE,
+      FROM_HERE,
+      base::Bind(&CreateAndStartFilePathWatcher,
+                 local_path,
                  google_apis::CreateRelayCallback(file_watcher_callback)),
-      base::Bind(&FileWatcher::OnWatcherStarted, weak_ptr_factory_.GetWeakPtr(),
+      base::Bind(&FileWatcher::OnWatcherStarted,
+                 weak_ptr_factory_.GetWeakPtr(),
                  callback));
 }