ash: Remove ShelfModel id conversion functions.

chrome/browser/ui/ash/launcher/extension_app_window_launcher_controller.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 "chrome/browser/ui/ash/launcher/extension_app_window_launcher_controller.h"
 
 #include "ash/public/cpp/shelf_types.h"
 #include "ash/public/cpp/window_properties.h"
 #include "ash/shelf/shelf_model.h"
 #include "ash/wm/window_util.h"
@@ skipping 135 matching lines @@
         app_controller_iter->second;
     DCHECK_EQ(controller->app_id(), shelf_id.app_id);
     controller->AddAppWindow(app_window);
   } else {
     std::unique_ptr<ExtensionAppWindowLauncherItemController> controller =
         base::MakeUnique<ExtensionAppWindowLauncherItemController>(shelf_id);
     app_controller_map_[shelf_id] = controller.get();
     controller->AddAppWindow(app_window);
 
     // Check for any existing pinned shelf item with a matching |shelf_id|.
-    const int item_index = owner()->shelf_model()->ItemIndexByID(shelf_id);
-    if (item_index < 0) {
+    if (owner()->GetItem(shelf_id) == nullptr) {
       owner()->CreateAppLauncherItem(std::move(controller), status);
       // Restore any existing app icon and flag as set.
       if (app_window->HasCustomIcon() && !app_window->app_icon().IsEmpty()) {
         owner()->SetLauncherItemImage(shelf_id,
                                       app_window->app_icon().AsImageSkia());
         app_controller_map_[shelf_id]->set_image_set_by_controller(true);
       }
     } else {
       owner()->shelf_model()->SetShelfItemDelegate(shelf_id,
                                                    std::move(controller));
@@ skipping 36 matching lines @@
 ExtensionAppWindowLauncherController::ControllerForWindow(
     aura::Window* window) {
   const auto window_iter = window_to_shelf_id_map_.find(window);
   if (window_iter == window_to_shelf_id_map_.end())
     return nullptr;
   const auto controller_iter = app_controller_map_.find(window_iter->second);
   if (controller_iter == app_controller_map_.end())
     return nullptr;
   return controller_iter->second;
 }