Reland of "file_manager: Migrate FILE thread to TaskScheduler"

chrome/browser/chromeos/file_manager/file_browser_handlers.cc

Index: chrome/browser/chromeos/file_manager/file_browser_handlers.cc
diff --git a/chrome/browser/chromeos/file_manager/file_browser_handlers.cc b/chrome/browser/chromeos/file_manager/file_browser_handlers.cc
index 381dc8f28070926f2424be798060a2ea5023a600..5f3df33371b42a59269bb5c14f6cd015233618f8 100644
--- a/chrome/browser/chromeos/file_manager/file_browser_handlers.cc
+++ b/chrome/browser/chromeos/file_manager/file_browser_handlers.cc
@@ -16,6 +16,7 @@
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/task_scheduler/post_task.h"
 #include "chrome/browser/chromeos/drive/file_system_util.h"
 #include "chrome/browser/chromeos/file_manager/app_id.h"
 #include "chrome/browser/chromeos/file_manager/fileapi_util.h"
@@ -218,7 +219,6 @@ FileBrowserHandlerExecutor::SetupFileAccessPermissions(
     scoped_refptr<storage::FileSystemContext> file_system_context_handler,
     const scoped_refptr<const Extension>& handler_extension,
     const std::vector<FileSystemURL>& file_urls) {
-  DCHECK_CURRENTLY_ON(BrowserThread::FILE);
   DCHECK(handler_extension.get());
 
   storage::ExternalFileSystemBackend* backend =
@@ -290,12 +290,9 @@ void FileBrowserHandlerExecutor::Execute(
   scoped_refptr<storage::FileSystemContext> file_system_context(
       util::GetFileSystemContextForExtensionId(profile_, extension_->id()));
 
-  BrowserThread::PostTaskAndReplyWithResult(
-      BrowserThread::FILE,
-      FROM_HERE,
-      base::Bind(&SetupFileAccessPermissions,
-                 file_system_context,
-                 extension_,
+  base::PostTaskWithTraitsAndReplyWithResult(
+      FROM_HERE, {base::MayBlock(), base::TaskPriority::USER_BLOCKING},
+      base::Bind(&SetupFileAccessPermissions, file_system_context, extension_,
                  file_urls),
       base::Bind(&FileBrowserHandlerExecutor::ExecuteAfterSetupFileAccess,
                  weak_ptr_factory_.GetWeakPtr()));