[TaskScheduler] Migrate bookmarks_api to use TaskScheduler.

BookmarksIOFunction used to retrieve default path in FILE
thread. Use a task with traits:
1. MayBlock: Since this requires IO
2. USER_VISIBLE: As this is part of importing/exporting bookmarks.
3. SKIP_ON_SHUTDOWN: There's no point to continue on or block shutdown
  because additional operations are required (e.g. showing a file
  select dialog) for this to complete.

Bug: 689520
Change-Id: Ibed8ea5213ca71f07a47cbb4e2c45cadeb9da429
Reviewed-on: https://chromium-review.googlesource.com/577112
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487976}

chrome/browser/extensions/api/bookmarks/bookmarks_api.cc

@@ -22,6 +22,7 @@
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/bookmarks/bookmark_html_writer.h"
@@ -742,37 +743,14 @@ BookmarksIOFunction::~BookmarksIOFunction() {
     select_file_dialog_->ListenerDestroyed();
 }
 
-void BookmarksIOFunction::SelectFile(ui::SelectFileDialog::Type type) {
-  // GetDefaultFilepathForBookmarkExport() might have to touch the filesystem
-  // (stat or access, for example), so this requires a thread with IO allowed.
-  if (!BrowserThread::CurrentlyOn(BrowserThread::FILE)) {
-    BrowserThread::PostTask(
-        BrowserThread::FILE, FROM_HERE,
-        base::BindOnce(&BookmarksIOFunction::SelectFile, this, type));
-    return;
-  }
-
-  // Pre-populating the filename field in case this is a SELECT_SAVEAS_FILE
-  // dialog. If not, there is no filename field in the dialog box.
-  base::FilePath default_path;
-  if (type == ui::SelectFileDialog::SELECT_SAVEAS_FILE)
-    default_path = GetDefaultFilepathForBookmarkExport();
-  else
-    DCHECK(type == ui::SelectFileDialog::SELECT_OPEN_FILE);
-
-  // After getting the |default_path|, ask the UI to display the file dialog.
-  BrowserThread::PostTask(
-      BrowserThread::UI, FROM_HERE,
-      base::BindOnce(&BookmarksIOFunction::ShowSelectFileDialog, this, type,
-                     default_path));
-}
-
 void BookmarksIOFunction::ShowSelectFileDialog(
     ui::SelectFileDialog::Type type,
     const base::FilePath& default_path) {
   if (!dispatcher())
     return;  // Extension was unloaded.
 
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+
   // Balanced in one of the three callbacks of SelectFileDialog:
   // either FileSelectionCanceled, MultiFilesSelected, or FileSelected
   AddRef();
@@ -813,7 +791,8 @@ void BookmarksIOFunction::MultiFilesSelected(
 bool BookmarksImportFunction::RunOnReady() {
   if (!EditBookmarksEnabled())
     return false;
-  SelectFile(ui::SelectFileDialog::SELECT_OPEN_FILE);
+  ShowSelectFileDialog(ui::SelectFileDialog::SELECT_OPEN_FILE,
+                       base::FilePath());
   return true;
 }
 
@@ -836,7 +815,17 @@ void BookmarksImportFunction::FileSelected(const base::FilePath& path,
 }
 
 bool BookmarksExportFunction::RunOnReady() {
-  SelectFile(ui::SelectFileDialog::SELECT_SAVEAS_FILE);
+  // "bookmarks.export" is exposed to a small number of extensions. These
+  // extensions use user gesture for export, so use USER_VISIBLE priority.
+  // GetDefaultFilepathForBookmarkExport() might have to touch filesystem
+  // (stat or access, for example), so this requires IO.
+  base::PostTaskWithTraitsAndReplyWithResult(
+      FROM_HERE,
+      {base::MayBlock(), base::TaskPriority::USER_VISIBLE,
+       base::TaskShutdownBehavior::SKIP_ON_SHUTDOWN},
+      base::BindOnce(&GetDefaultFilepathForBookmarkExport),
+      base::BindOnce(&BookmarksIOFunction::ShowSelectFileDialog, this,
+                     ui::SelectFileDialog::SELECT_SAVEAS_FILE));
   return true;
 }
 

chrome/browser/extensions/api/bookmarks/bookmarks_api.h

@@ -324,17 +324,13 @@ class BookmarksIOFunction : public BookmarksFunction,
                           void* params) override;
   void FileSelectionCanceled(void* params) override;
 
-  void SelectFile(ui::SelectFileDialog::Type type);
-
- protected:
-  ~BookmarksIOFunction() override;
-
- private:
   void ShowSelectFileDialog(
       ui::SelectFileDialog::Type type,
       const base::FilePath& default_path);
 
  protected:
+  ~BookmarksIOFunction() override;
+
   scoped_refptr<ui::SelectFileDialog> select_file_dialog_;
 };