Make launching apps from shelf more intuitive

ash/shelf/shelf.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/shelf/shelf.h"
 
 #include "ash/public/cpp/config.h"
 #include "ash/public/cpp/shelf_item_delegate.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/root_window_controller.h"
@@ skipping 256 matching lines @@
   // found (which is true when indexes_left is -1) or b.) the last item was
   // requested (which is true when index was passed in as a negative number).
   if (found_index >= 0 && (indexes_left == -1 || item_index < 0)) {
     // Then set this one as active (or advance to the next item of its kind).
     ActivateShelfItem(found_index);
   }
 }
 
 // static
 void Shelf::ActivateShelfItem(int item_index) {
+  ActivateShelfItemOnDisplay(item_index, display::kInvalidDisplayId);
+}
+
+// static
+void Shelf::ActivateShelfItemOnDisplay(int item_index, int64_t display_id) {
   ShelfModel* shelf_model = Shell::Get()->shelf_model();
   const ShelfItem& item = shelf_model->items()[item_index];
   ShelfItemDelegate* item_delegate = shelf_model->GetShelfItemDelegate(item.id);
   std::unique_ptr<ui::Event> event = base::MakeUnique<ui::KeyEvent>(
       ui::ET_KEY_RELEASED, ui::VKEY_UNKNOWN, ui::EF_NONE);
-  item_delegate->ItemSelected(std::move(event), display::kInvalidDisplayId,
-                              LAUNCH_FROM_UNKNOWN, base::Bind(&NoopCallback));
+  item_delegate->ItemSelected(std::move(event), display_id, LAUNCH_FROM_UNKNOWN,
+                              base::Bind(&NoopCallback));
 }
 
 bool Shelf::ProcessGestureEvent(const ui::GestureEvent& event) {
   // Can be called at login screen.
   if (!shelf_layout_manager_)
     return false;
   return shelf_layout_manager_->ProcessGestureEvent(event);
 }
 
 void Shelf::AddObserver(ShelfObserver* observer) {
@@ skipping 59 matching lines @@
 
 void Shelf::OnBackgroundUpdated(ShelfBackgroundType background_type,
                                 AnimationChangeType change_type) {
   if (background_type == GetBackgroundType())
     return;
   for (auto& observer : observers_)
     observer.OnBackgroundTypeChanged(background_type, change_type);
 }
 
 }  // namespace ash