Fix mouse scroll issue in folder

Changes:
Make apps grid view in folder handles all scroll event if folder is
opened to avoid closing app launcher via scrolling up in 1st page of
folder.

Bug: 847800
Change-Id: I5ec3744686202d519b421044d810857a3a5020d5
Reviewed-on: https://chromium-review.googlesource.com/1088148
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565052}

ui/app_list/views/apps_grid_view.cc

@@ -1759,9 +1759,11 @@ void AppsGridView::UpdateOpacity() {
 }
 
 bool AppsGridView::HandleScrollFromAppListView(int offset, ui::EventType type) {
-  // Scroll up at first page should close the launcher.
-  if (offset > 0 && !pagination_model()->IsValidPageRelative(-1))
+  // Scroll up at first page in top level apps grid should close the launcher.
+  if (!folder_delegate_ && offset > 0 &&
+      !pagination_model()->IsValidPageRelative(-1)) {
     return false;
+  }
 
   HandleScroll(offset, type);
   return true;