Fix Volume slider is captured in screenshot done in touchview mode

ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h

+// Copyright 2016 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 ASH_COMMON_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_SCREENSHOT_OBSERVER_H_
+#define ASH_COMMON_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_SCREENSHOT_OBSERVER_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+class ASH_EXPORT MaximizeModeScreenshotObserver {
+ public:
+  virtual ~MaximizeModeScreenshotObserver() {}
+
+  // Notifies when screenshot is going to be taken by volume-down modifier +
+  // power button accelerator combinations.

[Daniel Erat, 2016/07/28 23:57:52]

nit: delete "combinations"

[Qiang(Joe) Xu, 2016/07/29 04:30:31]

Done.

+  virtual void OnWillTakeScreenshotInMaximizeMode() = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_SCREENSHOT_OBSERVER_H_