Change ordering of Shell event handlers:

ash/drag_drop/drag_drop_controller.cc

Index: ash/drag_drop/drag_drop_controller.cc
diff --git a/ash/drag_drop/drag_drop_controller.cc b/ash/drag_drop/drag_drop_controller.cc
index 98e41d915c1b04c208a8d26e2b31ac357a60b2e6..40c7cec36348b602cf54e924877bcc5a04438ef3 100644
--- a/ash/drag_drop/drag_drop_controller.cc
+++ b/ash/drag_drop/drag_drop_controller.cc
@@ -148,7 +148,7 @@ DragDropController::DragDropController()
       drag_drop_window_delegate_(new DragDropTrackerDelegate(this)),
       current_drag_event_source_(ui::DragDropTypes::DRAG_EVENT_SOURCE_MOUSE),
       weak_factory_(this) {
-  Shell::GetInstance()->AddPreTargetHandler(this);
+  Shell::GetInstance()->PrependPreTargetHandler(this);
 }
 
 DragDropController::~DragDropController() {
@@ -226,12 +226,6 @@ int DragDropController::StartDragAndDrop(
   if (cancel_animation_)
     cancel_animation_->End();
 
-  // Become the first event handler since we should get first shot at handling
-  // any events during the drag drop session.
-  Shell::GetInstance()->RemovePreTargetHandler(this);
-  Shell::GetInstance()->PrependPreTargetHandler(this);
-
-
 #if !defined(OS_MACOSX)
   if (should_block_during_drag_drop_) {
     base::RunLoop run_loop(aura::Env::GetInstance()->GetDispatcher());