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

Review URL: https://codereview.chromium.org/298963004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273151 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 0 deletions

diff --git a/ui/views/view_model.cc b/ui/views/view_model.cc
index 5f492f5..a0a7549 100644
--- a/ui/views/view_model.cc
+++ b/ui/views/view_model.cc
@@ -33,6 +33,11 @@ void ViewModel::Remove(int index) {
 }
 
 void ViewModel::Move(int index, int target_index) {
+  DCHECK_LT(index, static_cast<int>(entries_.size()));
+  DCHECK_GE(index, 0);
+  DCHECK_LT(target_index, static_cast<int>(entries_.size()));
+  DCHECK_GE(target_index, 0);
+
   if (index == target_index)
     return;
   Entry entry(entries_[index]);