C++11 override style change for athena

ui/keyboard/keyboard_controller_observer.h

Index: ui/keyboard/keyboard_controller_observer.h
diff --git a/ui/keyboard/keyboard_controller_observer.h b/ui/keyboard/keyboard_controller_observer.h
index 2c7de7b016b4a00dafe86f6283c9da8aab48e597..174d06bb3507f924856d4586ff03c33382419368 100644
--- a/ui/keyboard/keyboard_controller_observer.h
+++ b/ui/keyboard/keyboard_controller_observer.h
@@ -17,6 +17,8 @@ namespace keyboard {
 // occur with the keyboard, such as the bounds or visiility changing.
 class KEYBOARD_EXPORT KeyboardControllerObserver {
  public:
+  virtual ~KeyboardControllerObserver() {}
+
   // Called when the keyboard bounds or visibility are about to change.
   virtual void OnKeyboardBoundsChanging(const gfx::Rect& new_bounds) = 0;
 };