Modify UMA for new style folder

Change:
Replace kOlderFolders with kFullscreenAppListFolders.

BUG=809324

Change-Id: Ib2f779fcd5e71a8e7a826c53b21ddaaf74126a22
Reviewed-on: https://chromium-review.googlesource.com/903412Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534812}

ui/app_list/views/app_list_main_view.cc

@@ -142,8 +142,8 @@ void AppListMainView::ActivateApp(AppListItem* item, int event_flags) {
   // TODO(jennyz): Activate the folder via AppListModel notification.
   if (item->GetItemType() == AppListFolderItem::kItemType) {
     contents_view_->ShowFolderContent(static_cast<AppListFolderItem*>(item));
-    UMA_HISTOGRAM_ENUMERATION(kAppListFolderOpenedHistogram, kOldFolders,
-                              kMaxFolderOpened);
+    UMA_HISTOGRAM_ENUMERATION(kAppListFolderOpenedHistogram,
+                              kFullscreenAppListFolders, kMaxFolderOpened);
   } else {
     base::RecordAction(base::UserMetricsAction("AppList_ClickOnApp"));
     delegate_->ActivateItem(item->id(), event_flags);