Enable swap primary accelerator only when possible

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index 955ba8e2352c314b3d85f4a53b3742379186a613..2ed2a555b62d8f2b3ef25517903b5d6713c25c0a 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -1050,8 +1050,9 @@ bool AcceleratorController::CanPerformAction(
     case TOUCH_HUD_CLEAR:
     case TOUCH_HUD_MODE_CHANGE:
       return CanHandleTouchHud();
+    case SWAP_PRIMARY_DISPLAY:
+      return gfx::Screen::GetScreen()->GetNumDisplays() > 1;
 #endif
-
     case CYCLE_BACKWARD_MRU:
     case CYCLE_FORWARD_MRU:
     case EXIT:
@@ -1099,7 +1100,6 @@ bool AcceleratorController::CanPerformAction(
     case OPEN_GET_HELP:
     case POWER_PRESSED:
     case POWER_RELEASED:
-    case SWAP_PRIMARY_DISPLAY:
     case TOGGLE_MIRROR_MODE:
     case TOGGLE_SPOKEN_FEEDBACK:
     case TOGGLE_WIFI: