ash: Add GetItemIndexForType() function to ShelfModel.

ash/shelf/shelf_model.cc

Index: ash/shelf/shelf_model.cc
diff --git a/ash/shelf/shelf_model.cc b/ash/shelf/shelf_model.cc
index b108a21f12c1c32523941d6ee3dd7af86fe005d3..d5d83f12e6a1001ad4bc7ca3fc351ea965cbdf3b 100644
--- a/ash/shelf/shelf_model.cc
+++ b/ash/shelf/shelf_model.cc
@@ -131,6 +131,14 @@ int ShelfModel::ItemIndexByID(LauncherID id) const {
   return i == items_.end() ? -1 : static_cast<int>(i - items_.begin());
 }
 
+int ShelfModel::GetItemIndexForType(LauncherItemType type) {
+  for (size_t i = 0; i < items_.size(); ++i) {
+    if (items_[i].type == type)
+      return i;
+  }
+  return -1;
+}
+
 LauncherItems::const_iterator ShelfModel::ItemByID(int id) const {
   for (LauncherItems::const_iterator i = items_.begin();
        i != items_.end(); ++i) {