Revert of mash: Remove ChromeLauncherController's |id_to_item_controller_map_|.

ash/common/shelf/shelf_model.cc

Index: ash/common/shelf/shelf_model.cc
diff --git a/ash/common/shelf/shelf_model.cc b/ash/common/shelf/shelf_model.cc
index acc2c10235b11c3835b4f25798c4d48db32aaa3f..640674ee66dee73a677e8067aab30557441963cf 100644
--- a/ash/common/shelf/shelf_model.cc
+++ b/ash/common/shelf/shelf_model.cc
@@ -70,7 +70,10 @@
   DCHECK(index >= 0 && index < item_count());
   ShelfItem old_item(items_[index]);
   items_.erase(items_.begin() + index);
-  id_to_item_delegate_map_.erase(old_item.id);
+  RemoveShelfItemDelegate(old_item.id);
+  // TODO(jamescook): Fold this into ShelfItemRemoved in existing observers.
+  for (auto& observer : observers_)
+    observer.OnSetShelfItemDelegate(old_item.id, nullptr);
   for (auto& observer : observers_)
     observer.ShelfItemRemoved(index, old_item);
 }
@@ -157,9 +160,14 @@
 void ShelfModel::SetShelfItemDelegate(
     ShelfID id,
     std::unique_ptr<ShelfItemDelegate> item_delegate) {
-  if (item_delegate)
-    item_delegate->set_shelf_id(id);
-  // This assignment replaces any ShelfItemDelegate already registered for |id|.
+  // If another ShelfItemDelegate is already registered for |id|, we assume
+  // that this request is replacing ShelfItemDelegate for |id| with
+  // |item_delegate|.
+  RemoveShelfItemDelegate(id);
+
+  for (auto& observer : observers_)
+    observer.OnSetShelfItemDelegate(id, item_delegate.get());
+
   id_to_item_delegate_map_[id] = std::move(item_delegate);
 }
 
@@ -195,4 +203,9 @@
   return index;
 }
 
+void ShelfModel::RemoveShelfItemDelegate(ShelfID id) {
+  if (id_to_item_delegate_map_.find(id) != id_to_item_delegate_map_.end())
+    id_to_item_delegate_map_.erase(id);
+}
+
 }  // namespace ash