Add support to the UI Service to run it inside the browser's process.

services/ui/ws/threaded_image_cursors.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SERVICES_UI_WS_THREADED_IMAGE_CURSORS_H_
+#define SERVICES_UI_WS_THREADED_IMAGE_CURSORS_H_
+
+#include "base/memory/weak_ptr.h"
+#include "ui/base/cursor/cursor.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace display {
+class Display;
+}
+
+namespace ui {
+class ImageCursors;
+class ImageCursorsSet;
+class PlatformWindow;
+
+namespace ws {
+
+// Wrapper around ui::ImageCursors, capable of executing its methods
+// asynchronously via the provided task runner.

[sky, 2017/07/13 17:14:58]

Please document why we need to step through these hoops.

[mfomitchev, 2017/07/13 17:53:06]

Done.

+class ThreadedImageCursors {
+ public:
+  // |resource_runner| is the task runner for the thread which can be used to
+  // load resources; |image_cursors_set_weak_ptr_| points to an object that
+  // lives on |resource_runner|'s thread.
+  // We create an ImageCursors object here and then pass the ownership to
+  // |image_cursors_set_weak_ptr_|. All operations on the ImageCursors object
+  // happen on |resource_runner|, which is why we need the owner to live on
+  // |resource_runner|'s thread.
+  ThreadedImageCursors(
+      scoped_refptr<base::SingleThreadTaskRunner>& resource_task_runner,
+      base::WeakPtr<ui::ImageCursorsSet> image_cursors_set_weak_ptr_);
+  ~ThreadedImageCursors();
+
+  // Executes ui::ImageCursors::SetDisplay asynchronously.
+  // Sets the display the cursors are loaded for. |scale_factor| determines the
+  // size of the image to load. Returns true if the cursor image is reloaded.
+  void SetDisplay(const display::Display& display, float scale_factor);
+
+  // Asynchronously sets the size of the mouse cursor icon.
+  void SetCursorSize(CursorSize cursor_size);
+
+  // Asynchronously sets the cursor type and then sets the corresponding
+  // PlatformCursor on the provided |platform_window|.
+  // |platform_window| pointer needs to be valid while this object is alive.
+  void SetCursor(ui::CursorType cursor_type,
+                 ui::PlatformWindow* platform_window);
+
+  // Helper method. Sets |platform_cursor| on the |platform_window|.
+  void SetCursorOnPlatformWindow(ui::PlatformCursor platform_cursor,
+                                 ui::PlatformWindow* platform_window);
+
+ private:
+  // The object used for performing the actual cursor operations.
+  // Created on UI Service's thread, but is used on the
+  // |resource_task_runner_|'s thread, because it needs to load resources.
+  base::WeakPtr<ui::ImageCursors> image_cursors_weak_ptr_;
+
+  // Task runner for the thread which owns the cursor resources.
+  // |image_cursors_set_weak_ptr__| and |image_cursors_weak_ptr_| should only
+  // be dereferenced on this task runner.
+  scoped_refptr<base::SingleThreadTaskRunner> resource_task_runner_;
+
+  // Task runner of the UI Service thread (where this object is created and
+  // destroyed).
+  scoped_refptr<base::SingleThreadTaskRunner> ui_service_task_runner_;
+
+  // Lives on |resource_runner_|'s thread, used to own the object behid
+  // |image_cursors_weak_ptr_|.
+  base::WeakPtr<ui::ImageCursorsSet> image_cursors_set_weak_ptr_;
+
+  base::WeakPtrFactory<ThreadedImageCursors> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadedImageCursors);
+};
+
+}  // namespace ws
+}  // namespace ui
+
+#endif  // SERVICES_UI_WS_THREADED_IMAGE_CURSORS_H_