Take a screenshot in maximize mode when volume down and power are pressed.

ash/wm/maximize_mode/maximize_mode_event_blocker.h

Index: ash/wm/maximize_mode/maximize_mode_event_blocker.h
diff --git a/ash/wm/maximize_mode/maximize_mode_event_blocker.h b/ash/wm/maximize_mode/maximize_mode_event_blocker.h
index 9e4a1a0bfa043fadc7e26af67621c719a8c173f6..71e7fa2b957b8410e8ff5276cb4129b5a323aefa 100644
--- a/ash/wm/maximize_mode/maximize_mode_event_blocker.h
+++ b/ash/wm/maximize_mode/maximize_mode_event_blocker.h
@@ -17,7 +17,9 @@ class Window;
 namespace ash {
 
 // A class which blocks mouse and keyboard events while instantiated by
-// replacing the root window event targeter.
+// replacing the root window event targeter. The replacement targeter also
+// handles a volume down + power keypress hotkey to take screenshots as the
+// keyboard cannot be used to do so.
 class MaximizeModeEventBlocker : public ShellObserver {
  public:
   MaximizeModeEventBlocker();