Remove ShelfItemDelegate::IsDraggable; check for app list button.

ash/common/shelf/shelf_view.cc

Index: ash/common/shelf/shelf_view.cc
diff --git a/ash/common/shelf/shelf_view.cc b/ash/common/shelf/shelf_view.cc
index 311b498fdf2822f4be81f5ed416f84610fca0145..686b841dadb9cb09d94d158f58b6d47c6817c13c 100644
--- a/ash/common/shelf/shelf_view.cc
+++ b/ash/common/shelf/shelf_view.cc
@@ -798,9 +798,7 @@ void ShelfView::PointerPressedOnButton(views::View* view,
   if (index == -1 || view_model_->view_size() <= 1)
     return;  // View is being deleted, ignore request.
 
-  ShelfItemDelegate* item_delegate =
-      model_->GetShelfItemDelegate(model_->items()[index].id);
-  if (!item_delegate->IsDraggable())
+  if (view == GetAppListButton())
     return;  // View is not draggable, ignore request.
 
   // Only when the repost event occurs on the same shelf item, we should ignore
@@ -1104,14 +1102,6 @@ void ShelfView::PrepareForDrag(Pointer pointer, const ui::LocatedEvent& event) {
     return;
   }
 
-  // If the item is no longer draggable, bail out.
-  ShelfItemDelegate* item_delegate =
-      model_->GetShelfItemDelegate(model_->items()[start_drag_index_].id);
-  if (!item_delegate->IsDraggable()) {
-    CancelDrag(-1);
-    return;
-  }
-
   // Move the view to the front so that it appears on top of other views.
   ReorderChildView(drag_view_, -1);
   bounds_animator_->StopAnimatingView(drag_view_);
@@ -1120,18 +1110,13 @@ void ShelfView::PrepareForDrag(Pointer pointer, const ui::LocatedEvent& event) {
 }
 
 void ShelfView::ContinueDrag(const ui::LocatedEvent& event) {
+  DCHECK(dragging());
+  DCHECK(drag_view_);
   // Due to a syncing operation the application might have been removed.
   // Bail if it is gone.
   int current_index = view_model_->GetIndexOfView(drag_view_);
   DCHECK_NE(-1, current_index);
 
-  ShelfItemDelegate* item_delegate =
-      model_->GetShelfItemDelegate(model_->items()[current_index].id);
-  if (!item_delegate->IsDraggable()) {
-    CancelDrag(-1);
-    return;
-  }
-
   // If this is not a drag and drop host operation and not the app list item,
   // check if the item got ripped off the shelf - if it did we are done.
   if (!drag_and_drop_shelf_id_ &&
@@ -1184,13 +1169,7 @@ void ShelfView::ContinueDrag(const ui::LocatedEvent& event) {
   target_index =
       std::min(indices.second, std::max(target_index, indices.first));
 
-  int first_draggable_item = 0;
-  while (first_draggable_item < static_cast<int>(model_->items().size()) &&
-         !model_->GetShelfItemDelegate(model_->items()[first_draggable_item].id)
-              ->IsDraggable()) {
-    first_draggable_item++;
-  }
-
+  int first_draggable_item = model_->GetItemIndexForType(TYPE_APP_LIST) + 1;

[James Cook, 2016/12/14 17:41:54]

Maybe comment or DCHECK that if the shelf only has the app list item then it's
impossible to drag, so first_draggable_item / target_index is always a valid
item?

[msw, 2016/12/14 19:46:50]

Added a comment and a couple DCHECKs. The top of this function also DCHECKs
dragging() and drag_view_, which is never set as the app list button itself
(drag_view_ is a ShelfButton and the app list button oddly isn't), and so if
drag_view_ is set, it must be some other valid draggable button (which comes
after the app list button, which is always first), so this index must be 1 and
must be valid. Really, I could just set this to 1, and DCHECK my assumptions,
but I'll leave the variable assignment as-is for now.

   target_index = std::max(target_index, first_draggable_item);
 
   if (target_index == current_index)