Enable virtual keyboard in overview mode

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 7d5ab3b680ae1f725e3e66a424752d5bc5b55a7f..89e7adb49352a8381503be10d46a19e0d694295a 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -141,6 +141,7 @@ class TouchTransformerController;
 class TouchObserverHUD;
 class UserActivityDetector;
 class UserWallpaperDelegate;
+class VirtualKeyboardObserver;
 class VideoActivityNotifier;
 class VideoDetector;
 class WebNotificationTray;
@@ -666,6 +667,7 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
   scoped_ptr<WindowSelectorController> window_selector_controller_;
   scoped_ptr<FocusCycler> focus_cycler_;
   scoped_ptr<DisplayController> display_controller_;
+  scoped_ptr<VirtualKeyboardObserver> virtual_keyboard_observer_;
   scoped_ptr<HighContrastController> high_contrast_controller_;
   scoped_ptr<MagnificationController> magnification_controller_;
   scoped_ptr<PartialMagnificationController> partial_magnification_controller_;