VR: Factor transient timing out of UiSceneManager.

chrome/browser/android/vr_shell/ui_elements/transience_manager.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 CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_TRANSIENCE_MANAGER_H_
+#define CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_TRANSIENCE_MANAGER_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/timer/timer.h"
+#include "chrome/browser/android/vr_shell/ui_elements/ui_element.h"
+
+namespace vr_shell {
+
+class TransienceManager {
+ public:
+  TransienceManager(UiElement* element, const base::TimeDelta& timeout)
+      : element_(element), timeout_(timeout) {

[bshe, 2017/06/27 14:57:09]

nit: move implementation to .cc file

[cjgrant, 2017/06/28 19:00:55]

Done.

+    element_->set_visible(false);
+  }
+
+  virtual ~TransienceManager() = default;
+
+  void SetEnabled(bool enabled);
+  void KickVisibility();

[bshe, 2017/06/27 14:57:09]

Perhaps name the function to showIfEnabled? It is not very obvious from the
function name that if it is not enabled, it wont be visible.

[cjgrant, 2017/06/28 19:00:55]

Done.  I use Kick instead of Show to keep the timer-specific part evident.

+  void EndVisibility();

[bshe, 2017/06/27 14:57:09]

Remove this too?

[cjgrant, 2017/06/28 19:00:55]

In this reworked version, we still need it.

+
+ private:
+  void StartTimer();
+  void OnTimeout();
+
+  UiElement* element_;
+  base::TimeDelta timeout_;
+  bool enabled_ = false;
+  base::OneShotTimer visibility_timer_;
+};
+
+}  // namespace vr_shell
+
+#endif  // CHROME_BROWSER_ANDROID_VR_SHELL_UI_ELEMENTS_TRANSIENCE_MANAGER_H_