Fix Volume slider is captured in screenshot done in touchview mode

ash/common/system/tray/system_tray_notifier.cc

Index: ash/common/system/tray/system_tray_notifier.cc
diff --git a/ash/common/system/tray/system_tray_notifier.cc b/ash/common/system/tray/system_tray_notifier.cc
index 3629b1bde5ff2b8785d6031453afa93459c32c73..5220d9f4fc02b7e7711e567b12946eae16392cde 100644
--- a/ash/common/system/tray/system_tray_notifier.cc
+++ b/ash/common/system/tray/system_tray_notifier.cc
@@ -10,6 +10,7 @@
 #include "ash/common/system/ime/ime_observer.h"
 #include "ash/common/system/update/update_observer.h"
 #include "ash/common/system/user/user_observer.h"
+#include "ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h"
 
 #if defined(OS_CHROMEOS)
 #include "ash/common/system/chromeos/bluetooth/bluetooth_observer.h"
@@ -142,6 +143,22 @@ void SystemTrayNotifier::NotifyLocaleChanged(LocaleObserver::Delegate* delegate,
       OnLocaleChanged(delegate, cur_locale, from_locale, to_locale));
 }
 
+void SystemTrayNotifier::AddMaximizeModeScreenshotObserver(
+    MaximizeModeScreenshotObserver* observer) {
+  maximize_mode_screenshot_observers_.AddObserver(observer);
+}
+
+void SystemTrayNotifier::RemoveMaximizeModeScreenshotObserver(
+    MaximizeModeScreenshotObserver* observer) {
+  maximize_mode_screenshot_observers_.RemoveObserver(observer);
+}
+
+void SystemTrayNotifier::NotifyWillTakeScreenshotInMaximizeMode() {
+  FOR_EACH_OBSERVER(MaximizeModeScreenshotObserver,
+                    maximize_mode_screenshot_observers_,
+                    OnWillTakeScreenshotInMaximizeMode());
+}
+
 void SystemTrayNotifier::AddUpdateObserver(UpdateObserver* observer) {
   update_observers_.AddObserver(observer);
 }