WIP - Gutterless resize on Windows

ui/accelerated_widget_mac/window_resize_helper_mac.h

-// Copyright 2015 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 UI_ACCELERATED_WIDGET_MAC_WINDOW_RESIZE_HELPER_MAC_H_
-#define UI_ACCELERATED_WIDGET_MAC_WINDOW_RESIZE_HELPER_MAC_H_
-
-#include "base/lazy_instance.h"
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "ui/accelerated_widget_mac/accelerated_widget_mac_export.h"
-
-namespace base {
-class SingleThreadTaskRunner;
-class TimeDelta;
-class WaitableEvent;
-}
-
-namespace ui {
-
-// WindowResizeHelperMac is used to make resize appear smooth. That is to
-// say, make sure that the window size and the size of the contents being drawn
-// in that window are resized in lock-step. This is accomplished by waiting
-// inside AppKit drawing routines on the UI thread for the compositor to produce
-// a frame of same size as the NSView that hosts an AcceleratedWidgetMac. When a
-// resize occurs, the view controller can wait for a frame of the correct size
-// by calling WindowResizeHelperMac::WaitForSingleTaskToRun() until a timeout
-// occurs, or the corresponding AcceleratedWidgetMac has a renderer frame of the
-// same size as its NSView.
-//
-// By posting tasks to the custom task_runner(), other threads indicate tasks
-// that are required to pick up a new frame. In the ordinary run of things these
-// would be posted to the |target_task_runner|; the UI thread given as an
-// argument to Init(). Posting instead to task_runner() will cause the tasks to
-// be posted to the UI thread (as usual), and will also enqueue them into a
-// queue which will be read and run in WaitForSingleTaskToRun(), potentially
-// before the task posted to the UI thread is run. Some care is taken (see
-// WrappedTask) to make sure that the messages are only executed once.
-//
-// This is further complicated because, in order for a frame to appear, it is
-// also necessary to run tasks posted by the ui::Compositor. To accomplish this,
-// the task_runner() that WindowResizeHelperMac provides can be used to
-// construct a ui::Compositor. When the Compositor posts tasks to it, they are
-// enqueued in the aforementioned queue, which may be pumped by
-// WindowResizeHelperMac::WaitForSingleTaskToRun().
-class ACCELERATED_WIDGET_MAC_EXPORT WindowResizeHelperMac {
- public:
-  static WindowResizeHelperMac* Get();
-
-  // Initializes the pumpable task_runner(), providing it with the task runner
-  // for UI thread tasks. task_runner() will be null before Init() is called,
-  // and WaitForSingleTaskToRun() will immediately return false.
-  void Init(
-      const scoped_refptr<base::SingleThreadTaskRunner>& target_task_runner);
-
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner() const;
-
-  // UI THREAD ONLY -----------------------------------------------------------
-
-  // Waits at most |max_delay| for a task to run. Returns true if a task ran,
-  // false if no task ran.
-  bool WaitForSingleTaskToRun(const base::TimeDelta& max_delay);
-
- private:
-  friend struct base::DefaultLazyInstanceTraits<WindowResizeHelperMac>;
-  WindowResizeHelperMac();
-  ~WindowResizeHelperMac();
-
-  // This helper is needed to create a ScopedAllowWait inside the scope of a
-  // class where it is allowed.
-  static void EventTimedWait(base::WaitableEvent* event, base::TimeDelta delay);
-
-  // The task runner to which the helper will post tasks. This also maintains
-  // the task queue and does the actual work for WaitForSingleTaskToRun.
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-
-  DISALLOW_COPY_AND_ASSIGN(WindowResizeHelperMac);
-};
-
-}  // namespace ui
-
-#endif  // UI_ACCELERATED_WIDGET_MAC_WINDOW_RESIZE_HELPER_MAC_H_