Fix Volume slider is captured in screenshot done in touchview mode

ash/wm/power_button_controller.h

Index: ash/wm/power_button_controller.h
diff --git a/ash/wm/power_button_controller.h b/ash/wm/power_button_controller.h
index 970ddab86dc8ce1bec159fa736c39dad267c7513..7043966f92a9d439ef664804e47343fab0d6804c 100644
--- a/ash/wm/power_button_controller.h
+++ b/ash/wm/power_button_controller.h
@@ -87,6 +87,12 @@ class ASH_EXPORT PowerButtonController
   // True when the volume down button is being held down.
   bool volume_down_pressed_;
 
+#if defined(OS_CHROMEOS)
+  // Volume to be restored after a screenshot is taken by pressing the power
+  // button while holding VKEY_VOLUME_DOWN.
+  int volume_percent_before_screenshot_;
+#endif
+
   // Has the screen brightness been reduced to 0%?
   bool brightness_is_zero_;