app_list: Fix possible out of bounds index.

app_list: Fix possible out of bounds index.

- Fix a problem that could not drop at the last position when dragging
  an item out of a folder;
- Fix a case view_model_.Move is called with an out of range target index
  when dragging the last item out of folder;
- Add a test for dragging last item and drop it at last slot;
- Speculative fix to protect using an index from data model to modify
   view_model_;
- A few more DCHECKs to catch the out-of-bound case; 

BUG=370064
TEST=AppListMainViewTest.DragLastItemFromFolderAndDropAtLastSlot

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=273151

[xiyuan, 2014-05-27 19:57:26]

jennyz@, app_list/*
sky@, for DCHECK in ViewModel::Move and you are welcome to review everything.

https://codereview.chromium.org/298963004/diff/120001/ui/app_list/views/apps_...
File ui/app_list/views/apps_grid_view.cc (right):

https://codereview.chromium.org/298963004/diff/120001/ui/app_list/views/apps_...
ui/app_list/views/apps_grid_view.cc:1716: if (target_model_index >=
deleted_folder_index)
This fixes the bad index for view_model_.Move below. It is needed because
model_->MoveItemToFolderAt removes |source_folder| from model and
|target_model_index| needs to be adjusted if |source_folder| is before
|target_model_index|.

https://codereview.chromium.org/298963004/diff/120001/ui/app_list/views/apps_...
ui/app_list/views/apps_grid_view.cc:1824: if
(!item_list_->FindItemIndex(last_item->id(), &last_item_index) ||
Speculative fix for calling view_model_.Add with a bad index.

https://codereview.chromium.org/298963004/diff/120001/ui/app_list/views/apps_...
ui/app_list/views/apps_grid_view.cc:2144: int last_possible_slot =
view_model_.view_size() % tiles_per_page();
No need to special case for dragging out of a folder. This allows dropping at
the last slot.

[jennyz, 2014-05-27 21:32:35]

lgtm. Thanks a lot for fixing the issue and adding the test case!

[sky, 2014-05-27 22:54:34]

LGTM - I'm also ok with making all the DCHECKs in this class CHECKs

[xiyuan, 2014-05-27 23:10:37]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2014-05-27 23:12:22]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/xiyuan@chromium.org/298963004/140001

[xiyuan, 2014-05-28 02:04:17]

The CQ bit was unchecked by xiyuan@chromium.org

[xiyuan, 2014-05-28 02:08:25]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2014-05-28 02:09:49]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/xiyuan@chromium.org/298963004/160001

[commit-bot: I haz the power, 2014-05-28 05:27:12]

Change committed as 273151